220-1101 Hardware Practice Question
A technician is replacing the power supply unit in a desktop computer. The new PSU is correctly rated for the system and the technician connects the 24-pin main motherboard connector and the 4+4 pin CPU power connector. When the power button is pressed, the system does not power on; no fans spin and no LEDs light up. The technician verifies that the PSU's power switch is on and that the wall outlet is functional. Using a multimeter, the technician confirms that the PSU outputs correct voltages on the 24-pin connector when the paperclip test is performed. Which of the following is the MOST likely cause of the issue?
⚠ Common exam trap
Candidates often assume a working paperclip test proves all connections are fine, but the test only checks the PSU output on the 24-pin connector and does not verify the EPS connector is properly seated or that the motherboard is receiving CPU power.
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 4+4 pin CPU power connector is not fully seated in the motherboard's EPS connector.
The 4+4 pin CPU power connector provides dedicated 12V power to the CPU VRM. If it is not fully seated, the motherboard's power delivery system will detect an open circuit and prevent the system from starting, even though the main 24-pin connector and PSU itself are functional. The paperclip test confirms the PSU can output correct voltages under no load, but it does not verify that the EPS connector is properly engaged.
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 PSU is not compatible with the motherboard's power requirements.
Why it's wrong here
The power supply is already verified as correctly rated for the system's load, and the paperclip test confirms the unit's primary outputs are live. Incompatibility would typically manifest as insufficient wattage, wrong form factor, or missing/unmatched connectors, none of which apply here because the correct main and CPU cables are present and the unit is rated appropriately.
- ✓
The 4+4 pin CPU power connector is not fully seated in the motherboard's EPS connector.
Why this is correct
The 4+4 pin EPS/ATX 12V connector supplies power to the CPU voltage regulator, and the motherboard's power-on sequence checks for a 'Power Good' signal from this rail. If this connector is partially seated, the CPU power circuit is incomplete, so the board won't initialize even though the 24-pin main connector is live and the PSU fan spins. A properly seated 4+4 pin connector will click into place; it is a common oversight when the connector is not pressed down firmly.
- ✗
The motherboard is shorting against the case.
Why it's wrong here
A motherboard short against the case usually causes the system to power on for a second then shut down, or to emit a burning smell, not to remain completely silent. Because the paperclip test and the 24-pin connector indicate the PSU is delivering standby power, a short would likely trip overcurrent protection or start a fan spin before shutting down. The absence of any activity, including no fan spin from the CPU or case fans, points to a missing power connection rather than a short.
- ✗
The power button header is connected to the wrong pins.
Why it's wrong here
Incorrect front-panel header wiring would cause the power button to have no effect, but the technician verified the PSU starts with a paperclip, and typically a wrong header connection would not prevent the motherboard from powering on via a direct jumper on the power pins. The most common cause of a completely dead board after a PSU replacement is an unseated CPU power connector, not a reversed power LED connector. Still, if the CPU power connector were fully seated and the board remained dead, checking the front panel header is a valid next step, but it is not the primary failure here.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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