220-1101 Hardware Practice Question
A technician builds a new desktop computer. After pressing the power button, the system powers on for about 5 seconds, then shuts down, and then immediately attempts to power on again, repeating the cycle. The technician has verified that all power connections are secure and has reseated the CPU and RAM. Which of the following should the technician check NEXT?
⚠ Common exam trap
The trap here is that candidates often focus on power supply or front panel connections because the symptom sounds like a power issue, but the timed 5-second cycle is the key indicator of thermal protection, not a power supply fault.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The CPU heatsink fan connection
The symptom of a system powering on for a few seconds, then shutting down and immediately rebooting in a cycle is classic behavior of a thermal or overheat protection trigger. The CPU heatsink fan connection (option B) is the most likely cause because if the fan is not connected or is faulty, the CPU rapidly overheats, causing the motherboard's thermal protection circuitry to shut down the system; it then attempts to restart, only to overheat again, creating the loop. The technician has already reseated the CPU and RAM, so the next logical step is to verify the CPU cooler's power connection.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The power supply voltage selector switch
Why it's wrong here
An ATX power supply's manual voltage selector must match the local mains (e.g., 115V AC vs 230V AC). If it is set to 110V while plugged into a 220V outlet, overvoltage protection typically trips immediately, causing the unit to latch off before the CPU even starts — or, in older units, catastrophic failure. If set to 220V on 110V, the PSU will fail to produce stable outputs, so the system won't begin a normal POST at all; neither condition yields a healthy boot followed seconds later by a shutdown and restart cycle.
- ✓
The CPU heatsink fan connection
Why this is correct
Modern motherboards monitor the CPU fan tachometer and CPU temperature through the CPU_FAN header and on-die thermal sensors. If the CPU heatsink fan is left disconnected, the CPU heats up to its thermal threshold within a few seconds, so the motherboard's thermal protection shuts down power to the CPU before permanent damage. The system then restarts, only to heat up again, creating the brief power-on/off cycle seen here. Many boards will also halt at a 'CPU Fan Error' screen, but the cycling symptom is classic when BIOS is set to auto-start after power loss.
- ✗
The front panel power switch header
Why it's wrong here
The front panel power switch header simply connects the case's momentary push button to the motherboard's soft-power-on pins. If this header is incorrectly wired, shorted, or the switch is stuck open, the motherboard typically won't receive the correct PWRBTN# assertion to transition from S5 to S0, so the system never starts or turns off immediately when the button is released. A successful POST that runs for several seconds then cycles is caused by a hardware-triggered shutdown (like thermal failure), not by the switch header, which only presents a contact bounce signal at startup.
- ✗
The CMOS battery
Why it's wrong here
The CMOS coin cell battery exclusively keeps the real-time clock and retains BIOS/UEFI configuration data in volatile CMOS RAM while the system is unplugged. If it's dead or missing, the board can still POST using default BIOS settings but will show time/date resets, 'CMOS checksum error,' or 'Press F1' prompts; it does not participate in the power-good or thermal shutdown circuits. Therefore, a depleted CMOS battery cannot interrupt a running POST or cause the CPU to lose power after a few seconds — the system would continue running normally until the AC power is removed.
Go deeper
Related to this question
Learn chapter
Thermal Paste Application
Key term
RAM
RAM (Random-Access Memory) is volatile computer memory that temporarily stores data for quick access by the CPU.
Key term
Dual In-line Memory Module
A Dual In-line Memory Module (DIMM) is a small circuit board that holds memory chips and plugs into a computer's motherboard to provide Random Access Memory (RAM).
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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