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220-1201 Practice Question: A customer reports that their desktop PC will not…
A customer reports that their desktop PC will not power on at all. The power supply fan does not spin, and no LEDs are lit. You have verified the power cord is good and the outlet has power. Which motherboard component should you check first?
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 24-pin ATX power connector
The ATX power connector (main power connector) supplies power from the PSU to the motherboard. If it is loose or disconnected, the motherboard will not receive power, causing a no-power condition. Always check this first before assuming PSU failure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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The CMOS battery
Why it's wrong here
The CMOS battery provides continuous power to the motherboard's Real-Time Clock (RTC) and the non-volatile BIOS memory (CMOS RAM) when the system is powered off or unplugged. While a dead CMOS battery can lead to issues like incorrect date/time or lost BIOS settings, it does not prevent the Power Supply Unit (PSU) from receiving AC power or attempting to deliver DC power to the motherboard if the main connections are intact. Therefore, a non-spinning PSU fan indicates a more fundamental power delivery problem, not merely a depleted CMOS battery.
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The front panel power switch header
Why it's wrong here
The front panel power switch header connects the physical power button to the motherboard, signaling it to initiate the power-on sequence when pressed. A faulty switch or a loose connection at this header would prevent the system from responding to the power button, but the Power Supply Unit (PSU) would still receive standby power and its fan might briefly spin during a power-on self-test if the main 24-pin ATX power connector is properly seated. A completely inactive PSU fan points to a lack of primary power delivery, not just a failed input signal from the front panel.
- ✓
The 24-pin ATX power connector
Why this is correct
The 24-pin ATX power connector is the primary and most critical connection from the Power Supply Unit (PSU) to the motherboard, supplying all essential voltage rails (+3.3V, +5V, +12V, etc.) required for the motherboard and its integrated components to function. If this crucial connector is loose or completely disconnected, the motherboard will not receive any operational power, preventing it from initiating the boot sequence or even drawing sufficient standby power. Consequently, the PSU fan, which typically spins when the PSU is actively delivering power or during initial self-tests, would remain inactive, clearly indicating a fundamental power delivery failure.
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The CPU fan header
Why it's wrong here
The CPU fan header on the motherboard is solely dedicated to providing power and control signals for the CPU cooling fan, regulating its speed based on processor temperature. A loose or disconnected CPU fan header would only result in the CPU fan not spinning, potentially leading to CPU overheating and system shutdown after boot, but it has no direct impact on the overall primary power delivery from the Power Supply Unit (PSU) to the motherboard. Therefore, it cannot be the cause of a completely inactive PSU fan, which signifies a broader power issue.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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