Build safely
Use ESD controls, proper component handling, power-off procedures, organized tools, and teacher safety checkpoints.
CompTIA A+ • Mission 04
Build the PC: From Parts to POST
This week you will assemble a brand-new desktop PC. The goal is not to race. Work like an IT technician: protect components, verify compatibility, install one system at a time, inspect your work, and prove the computer can complete POST before you call the build successful.
A+ quick navigation
About the Practice PC Build Guide: this is a learning checklist and documentation guide for your classroom PC build. It is not a customer work order, repair request, or ticket. Use it to slow down, verify each step, and capture evidence of what you installed.
Mission outcomes
What you should be able to do by the end.
Build compatibly
Match CPU/socket, RAM generation, storage interface, case/motherboard form factor, PSU capacity/connectors, cooling, and expansion requirements.
Build logically
Install CPU/cooling, RAM, storage, motherboard, power supply, expansion devices, internal connections, and case wiring in a controlled sequence.
Explain the system
Explain what each installed device does and how power, data, heat, and physical connections work together.
Reach POST
Inspect the machine before first power, observe POST/UEFI behavior, and distinguish a hardware-startup problem from an operating-system problem.
Think like A+
Recognize parts by sight, compare options, select BEST/NEXT actions, and troubleshoot symptoms using evidence instead of random replacement.
Mission 04 aligns to CompTIA A+ Core 1 (220-1201) objectives covering motherboard components and connectors, processors, memory, storage, power supplies, cooling, expansion hardware, component compatibility, and hardware installation/troubleshooting. [Sources 1–2]
Safety gate
Protect the person. Protect the parts.
Memory trick: ESD protects the PARTS. Electrical safety protects the PERSON.
Electrostatic discharge (ESD) can damage sensitive electronic components. The CompTIA A+ exam objectives include ESD straps, ESD mats, equipment grounding, antistatic bags, proper component handling, and disconnecting power before PC repair. These are certification skills you are practicing during this build. [Sources 1–2]
For our BRAND-NEW, never-powered build
Clean workspace. Remove unnecessary plastic, loose packaging, drinks, and clutter.
Wear the ESD wrist strap on bare skin. It should make reliable contact with your wrist.
Connect only to the instructor-approved ESD grounding point. Use the designated ESD mat/workstation connection or other approved point.
Keep sensitive parts protected. Leave RAM, CPU, M.2 devices, GPUs, and boards in antistatic packaging until needed.
Handle boards by the edges. Avoid touching gold contacts, socket pins, chips, and exposed connector contacts. Intel gives the same handling guidance for M.2 devices. [Source 3]
Build de-energized. In this class, connect AC power only after the build passes the pre-power inspection and the instructor authorizes first power.
STOP: An ESD strap is not protection from hazardous electrical current. For this classroom build, ESD straps are used while the computer is disconnected from mains power and students are handling de-energized components.
FYI: If you later service a PC that HAS been powered before
Shut down→Disconnect AC power→Follow model service procedure→Verify de-energized→Apply ESD controls
Some manufacturer service manuals direct technicians to hold the power button after external power is disconnected to drain residual system power. Dell, for example, documents a 15–20 second procedure on several desktop models. Do not assume the exact procedure is identical for every system: use the manufacturer service manual for the model you are servicing. [Source 4]
Never open a PSU enclosure in this class. Unplugging the computer does not make the inside of a power-supply unit student-serviceable. Treat the PSU as a replaceable module.
Phase 1
Compatibility check before installation.
A component can look right and still be wrong for the system. Use the Practice PC Build Guide to record the actual parts in your build.
CPU ↔ motherboard
The motherboard socket/platform must support the CPU. Do not force a processor into a socket.
Memory: CPU SITS in a SOCKET.
RAM ↔ motherboard
Match the supported DDR generation, module type, capacity, and recommended slot/channel arrangement.
Memory: RAM SLIDES into a SLOT.
Storage ↔ interface
Know whether the drive needs SATA data + SATA power or uses an M.2 slot. M.2 and NVMe are not synonyms.
M.2 = SHAPE. NVMe = TALK.
PSU ↔ load
Verify capacity, form factor, and required connectors. CompTIA emphasizes matching power needs to the PSU and recognizing efficiency ratings. [Source 2]
Cooler ↔ CPU/case
Verify cooler mounting compatibility, thermal-interface material, fan/pump connection, and physical clearance.
Case ↔ motherboard
Verify form factor, standoff positions, expansion clearance, airflow, drive mounting, and cable routing.
Phase 2
Build one subsystem at a time.
1
Install the CPU
Identify the socket, verify orientation/alignment marks, open the retention mechanism, lower/place the CPU without force, then secure it according to the board/socket design. CompTIA A+ Core 1 exam objective 3.5 includes CPU installation, socket types, motherboard compatibility, add-on cards, cooling, and related hardware installation skills. [Source 1]
Teacher checkpoint: verify CPU model, socket, and orientation before securing the retention mechanism.
2
Install the thermal solution
Use the cooler/manufacturer instructions. Thermal paste or a pre-applied thermal interface fills microscopic gaps so heat transfers more effectively from CPU to cooler. A heat sink provides surface area; fans provide active airflow. [Source 2]
Memory: CPU makes HEAT → thermal material improves CONTACT → heat sink SPREADS heat → fan MOVES heat away.
3
Install RAM
Confirm the DDR generation and DIMM orientation. Open the latches as designed, align the notch, and press evenly until the module is fully seated. Use the motherboard manual for the recommended slots when installing a matched pair. CompTIA A+ Core 1 exam objective 3.1 includes DDR generations, DIMM characteristics, and memory channel configurations. [Source 1]
A+ clue: a module that is partly seated can create no-POST or memory-related symptoms. Do not force incompatible memory.
4
Install storage
M.2: use the correct slot/standoff and secure the module level without excessive pressure. SATA drive: mount the drive securely; later it needs SATA DATA to the motherboard and SATA POWER from the PSU. CompTIA A+ Core 1 exam objective 3.4 includes HDDs, SSDs, SATA, PCIe/M.2/NVMe storage, removable storage, optical drives, and RAID concepts. [Sources 1, 3]
Memory: Motherboard TALKS to SATA drive through DATA. PSU FEEDS it through POWER.
5
Mount the motherboard
Check the case standoffs before lowering the board into place. Align rear I/O as required by the case/board design and secure the motherboard without overtightening. Keep loose screws out from under the board.
STOP and inspect: incorrect standoff placement can physically damage the board or create an unwanted electrical contact.
6
Install the power supply
Mount the PSU in the supported orientation and consider airflow. CompTIA A+ Core 1 exam objective 3.6 includes power-supply selection and installation, wattage, efficiency, 20+4-pin motherboard power, modular designs, and related power requirements. [Source 1]
7
Install expansion devices
Install the GPU or other required PCIe device in the appropriate slot, secure the bracket, and connect supplemental power if the device requires it. PCIe is the expansion highway; the number of lanes affects available bandwidth.
Memory: PCIe = EXPANSION HIGHWAY. A GPU commonly uses the long x16 physical slot.
8
Connect power, data, headers, and fans
Use the motherboard and component manuals. Typical connections include 24-pin motherboard power, CPU power, GPU power when required, SATA power/data, CPU fan, case fans, front-panel power/reset/LED connections, front USB, and front audio.
Distinction trick: PORT = portal outside • HEADER = hidden inside • CONNECTOR = broad connection term • INTERFACE = connection/communication system.
9
Manage airflow and cables
Keep cables away from fans and airflow pathways. CompTIA describes cool air entering from front/side locations and hot exhaust leaving the rear/top as a common airflow model. [Source 2]
Cool air IN→Components absorb/use power→Heat moves to cooler/air→Hot air OUT
Phase 3
Pre-power inspection: do not press the button yet.
CPU is seated and retention mechanism is secured.
Cooler is mounted correctly; CPU fan/pump connection is correct.
RAM is fully seated in the intended slots.
M.2/storage device is secured; SATA data/power are present if required.
24-pin motherboard power is fully seated.
CPU power connector is fully seated.
GPU is secured and supplemental power is connected if required.
Front-panel and internal headers are checked against the motherboard manual.
No loose screws or conductive debris are under/on the motherboard.
No cable can contact a fan blade.
Monitor is connected to the correct video output for this build.
Peer inspection is complete and instructor authorization is received.
Teacher Safety Gate: first AC connection and first power-on happen only after the instructor approves the build.
Phase 4
First power: POST before operating system.
Power applied→Fans / indicators→POST→Display→UEFI/BIOS→Boot device
POST = Power-On Self-Test. A machine can successfully reach firmware setup even if no operating system is installed yet. The first build goal is a stable hardware startup and useful display/firmware access—not an immediate Windows desktop.
During first power: keep hands out of the case. Observe fans, LEDs, display, POST/diagnostic indicators, and firmware behavior.
If something is wrong: power down, disconnect external AC power, follow the correct de-energizing procedure, then troubleshoot. Do not reach into an energized build and start reseating components.
Troubleshooting bridge
If it does not POST, use evidence.
No power at all
Check external AC, PSU switch if present, case power-switch header, 24-pin power, CPU power, and installation evidence before replacing major parts.
Power but no display
Check monitor power/input/cable, correct display output, GPU seating/power if used, RAM seating, and POST indicators.
Starts then overheats/shuts down
Investigate cooler contact, thermal interface, CPU fan/pump operation, and airflow before blaming storage or networking.
Storage not detected
Check the correct M.2 slot/support or SATA data/power connections, firmware detection, and physical installation.
Memory problem
Verify compatibility, correct slots, full seating, and one-change-at-a-time testing.
Document it
Record symptom → evidence → theory → action → result. Mission 5 will turn this build into a formal hardware-troubleshooting investigation.
PBQ mindset: an A+ task may ask you to identify a component from an image, match a cable to a connector, select compatible hardware, arrange installation steps, or choose the BEST/NEXT response to a symptom.
Memory tricks
Keep the high-value distinctions.
Socket vs. slot
CPU SITS in a SOCKET.
RAM/cards SLIDE into SLOTS.
M.2 vs. NVMe
M.2 = SHAPE.
NVMe = TALK.
M.2 is a form factor; NVMe is a storage protocol commonly using PCIe.
SATA
S = STORAGE.
Motherboard talks through SATA DATA; PSU feeds through SATA POWER.
Power connectors
24-pin = MAIN MEAL for the motherboard.
CPU power = BRAIN FOOD.
Cooling
CONTACT → SPREAD → MOVE.
Thermal material improves contact, heat sink spreads heat, fan/liquid system moves it away.
First startup
POST before OS.
Prove the hardware can initialize before troubleshooting Windows that is not installed yet.
A+ notebook evidence
Capture the system—not every sentence.
Recommended Mission 4 spread: draw or paste one large image of your completed PC. Use arrows to label CPU, cooler, RAM, storage, motherboard, PSU, GPU/expansion, intake, exhaust, 24-pin power, CPU power, and one internal header. Add a tiny compatibility chain and one box titled How could A+ ask this?
Do not make a copied spec sheet. Record the facts you need to recognize, compare, install, troubleshoot, and retrieve quickly.
Mission check
Try the decision before reading the explanation.
1. A new PC powers on, but the display remains blank. The build uses a discrete GPU. What is the BEST early check?
Best answer: B. Start with the evidence and simple display-path checks before replacing major hardware.
2. A technician is installing a 2.5-inch SATA SSD. Which connections are normally required?
Best answer: C. The motherboard communicates with a SATA drive over SATA data; the PSU supplies SATA power.
3. CPU temperature rises quickly immediately after first startup. What should the technician investigate FIRST?
Best answer: D. The symptom directly points to the cooling path.
Sources & A+ exam objective alignment
- CompTIA A+ Core 1 (220-1201) V15 Exam Objectives. Mission 4 prepares you for objective 3.1 (RAM), 3.4 (storage devices), 3.5 (motherboards, CPUs, add-on cards, cooling, and compatibility), 3.6 (power supplies), 5.1 (motherboard/RAM/CPU/power troubleshooting), and 5.2 (storage troubleshooting).
- CompTIA A+ Core 2 (220-1202) V15 Exam Objectives — 4.4 Common Safety Procedures. Includes ESD straps/mats, equipment grounding, proper component handling/storage, antistatic bags, cable management, and disconnecting power before PC repair.
- Intel: Proper Handling Techniques and Precautions for Your M.2 Device. Reinforces antistatic storage, grounding/ESD precautions, handling devices by the sides, avoiding gold contacts, and correct M.2 installation.
- Dell XPS 8960 Service Manual: Drain residual flea power. Example manufacturer procedure for a previously powered desktop. Always follow the service manual for the actual computer being serviced.
FamilyPD independently creates its explanations, memory tricks, activities, and original practice questions. This page is a certification-prep study aid and classroom build guide, not an official CompTIA product. Hardware procedures vary by model; the manufacturer instructions for the actual motherboard, CPU, cooler, case, PSU, storage, and GPU take priority.