PC Shuts Down Seconds After Power On: Check CPU Fan Header
A technician replaced a failed power supply in a desktop computer with a higher wattage unit. The computer now powers on for one second then shuts down. The technician has verified all cable connections are secure and the PSU passes the paperclip test. What should the technician check NEXT?
⚠ Common exam trap
Many candidates assume a failed PSU replacement is always a DOA unit, but the paperclip test passes, so they overlook the voltage selector switch — a common oversight when reusing a PSU from a different region or model.
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 voltage selector switch on the PSU.
The voltage selector switch on the PSU must match the local mains voltage (115V for North America, 230V for Europe/Asia). If set to 230V while plugged into a 115V outlet, the PSU will briefly start but immediately shut down due to undervoltage protection. The paperclip test only verifies the PSU fan spins, not that it delivers correct voltages under load.
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 motherboard BIOS settings.
Why it's wrong here
BIOS settings are stored in non-volatile memory and only take effect after the CPU and chipset start executing POST, which occurs well after the PSU has delivered stable rails and asserted a power-good signal. An immediate shutdown at the one-second mark typically happens before POST completes, often due to a protection circuit reacting to an input-side fault rather than to firmware configuration. While a misconfigured BIOS can cause a boot loop or shutdown under load, it cannot turn off the PSU one second after power-on when the PSU is already in a protection shutdown state. Therefore, BIOS settings are not the cause of this instant loss of output power.
When this WOULD be correct
If a computer powers on but fails to boot or exhibits intermittent shutdowns after a component change, checking BIOS settings (e.g., power management, boot order) would be appropriate. For example, after upgrading a CPU, incorrect BIOS settings might cause instability.
- ✓
The voltage selector switch on the PSU.
Why this is correct
The voltage selector switch must match the local mains voltage. If it is set to 115 V while plugged into a 230 V outlet, the input rectifier and filter capacitors are subjected to roughly double the intended voltage, causing the PSU’s overvoltage protection circuit to quickly shut down the DC outputs—often within a second after the fan spins up. An incorrect 115 V setting on a 230 V mains supply will trigger this protection even if the PSU itself is fully functional, and this exactly matches the symptom seen after a power supply replacement.
- ✗
The CPU fan header connection.
Why it's wrong here
If the CPU fan header is not connected, the system may shut down after a few seconds due to CPU overheating, but typically the system stays on longer than one second. Also, the fan header does not affect the initial power-on cycle.
- ✗
The front panel power switch.
Why it's wrong here
A faulty front panel power switch is a possible cause of unintended shutdown, but it would not produce a consistent one-second-on-then-off pattern because the switch is just a momentary contact that signals the motherboard. If the switch were stuck closed, the motherboard would normally force a power-off only after a 4-second press-and-hold, not immediately, and the paperclip test bypasses the switch entirely by directly jumping PS_ON to ground. Since the paperclip test proved the PSU can stay on, the immediate shutdown is far more consistent with the PSU’s input voltage selector being wrong than with a switch that merely toggles the power signal.
When this WOULD be correct
If the computer does not power on at all (no fans, no lights) and the PSU passes the paperclip test, the technician should check the front panel power switch connection to the motherboard header as a possible open circuit.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 220-1101 exam frequently reuses these exact scenarios with slightly different constraints.
✓The voltage selector switch on the PSU.Correct answer▾
Why this is correct
The voltage selector switch must match the local mains voltage. If it is set to 115 V while plugged into a 230 V outlet, the input rectifier and filter capacitors are subjected to roughly double the intended voltage, causing the PSU’s overvoltage protection circuit to quickly shut down the DC outputs—often within a second after the fan spins up. An incorrect 115 V setting on a 230 V mains supply will trigger this protection even if the PSU itself is fully functional, and this exactly matches the symptom seen after a power supply replacement.
✗The motherboard BIOS settings.Wrong answer — click to see why▾
Why this is wrong here
The motherboard BIOS settings do not cause a system to power on for one second then shut down immediately after a PSU replacement; such behavior typically indicates a hardware power issue, not a configuration problem.
★ When this WOULD be the correct answer
If a computer powers on but fails to boot or exhibits intermittent shutdowns after a component change, checking BIOS settings (e.g., power management, boot order) would be appropriate. For example, after upgrading a CPU, incorrect BIOS settings might cause instability.
Why candidates choose this
Candidates may assume that a higher wattage PSU requires BIOS adjustment for power delivery, or they might think the BIOS controls power-on behavior, leading them to check settings first.
✗The front panel power switch.Wrong answer — click to see why▾
Why this is wrong here
The front panel power switch is a momentary contact switch that signals the motherboard to power on; it does not cause a shutdown after one second if the system powers on initially. The issue is likely power-related, not a faulty switch.
★ When this WOULD be the correct answer
If the computer does not power on at all (no fans, no lights) and the PSU passes the paperclip test, the technician should check the front panel power switch connection to the motherboard header as a possible open circuit.
Why candidates choose this
Candidates may think a faulty power switch could cause intermittent shutdowns, but the switch only sends a brief signal; once the system is on, the switch is not involved in maintaining power.
Analysis generated from the official 220-1101blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
Related to this question
About these practice questions
One of 896 original 220-1101 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1101 exam.