220-1101 Hardware and Network Troubleshooting Practice Question
After a power outage, a desktop computer will not power on. The PSU fan does not spin, and no LEDs are lit. The technician tests the power supply with a PSU tester; all voltages are within spec. A multimeter reading at the motherboard's power button header shows 3.3V when the button is pressed. The power supply is also confirmed to work when tested in another system. What is the most likely cause?
⚠ Common exam trap
Watch out — candidates often assume a working PSU tester and a successful test in another system guarantee the PSU is the cause, but they overlook that the motherboard must actively command the PSU to start via the PS_ON# signal.
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 motherboard has failed
The motherboard has failed because the PSU passes all voltage tests and works in another system, yet the desktop shows no signs of power (no fan spin, no LEDs) when connected to this motherboard. The 3.3V reading at the power button header indicates the motherboard is receiving standby power and the button is functioning, but the motherboard is not completing the power-on sequence (pulling PS_ON# low) to start the PSU. This points to a failed motherboard, likely a short or damaged power regulation circuit.
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 has failed
Why this is correct
Given that the PSU is good and the power button sends the correct signal, the motherboard is the remaining component that controls the power-on sequence. A damaged motherboard (e.g., from a power surge) will not start the system.
- ✗
The power supply is still faulty despite the tester showing good voltages
Why it's wrong here
The power supply has been objectively verified through a PSU tester and by successfully powering a known-good system; both tests confirm it can deliver correct voltages and sufficient current on all rails. With the +5VSB standby rail functioning to produce the 3.3V signal at the power button, the PSU is providing the essential power needed for the start-up sequence. Therefore, the claim that the PSU is still faulty despite passing these checks is contradicted by direct evidence and not the correct diagnosis.
When this WOULD be correct
In a scenario where the PSU tester shows normal voltages but the PSU fails to power on in any system, or where the PSU tester itself is known to give false positives, then a faulty PSU would be the correct answer.
- ✗
The power button is faulty
Why it's wrong here
The multimeter reading of 3.3V when the power button is pressed proves the switch contacts are closing properly, sending a valid high-to-low or low-to-high signal (depending on the motherboard design) to the front-panel header. A faulty button would fail to generate this voltage transition or would show a constant open circuit with 0V. Since the correct signal is reaching the motherboard, the button is definitively not the cause; the fault must lie downstream in the motherboard's power-on logic, such as a damaged Super I/O chip or trace.
When this WOULD be correct
A desktop computer does not power on; pressing the power button yields no response, and a multimeter at the power button header shows 0V when the button is pressed, while the power supply passes a PSU tester. In this scenario, the power button is faulty.
- ✗
The BIOS has become corrupted
Why it's wrong here
BIOS corruption typically prevents the system from booting or causes POST failures, but the system should still attempt to power on (fans spin, LEDs light). No power activity at all points to a hardware power path failure, not BIOS.
When this WOULD be correct
In a scenario where a computer powers on (fans spin, LEDs light) but fails to boot, displays a black screen, or beeps repeatedly, and the PSU and other hardware test fine, a corrupted BIOS could be the cause. For example, after a failed BIOS update or power outage during a flash.
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 motherboard has failedCorrect answer▾
Why this is correct
Given that the PSU is good and the power button sends the correct signal, the motherboard is the remaining component that controls the power-on sequence. A damaged motherboard (e.g., from a power surge) will not start the system.
✗The power supply is still faulty despite the tester showing good voltagesWrong answer — click to see why▾
Why this is wrong here
The PSU tester shows all voltages within spec, and the PSU works in another system, so it is not faulty. The issue is that the motherboard does not power on despite receiving proper voltage from the PSU and a valid power button signal.
★ When this WOULD be the correct answer
In a scenario where the PSU tester shows normal voltages but the PSU fails to power on in any system, or where the PSU tester itself is known to give false positives, then a faulty PSU would be the correct answer.
Why candidates choose this
Candidates may distrust the PSU tester results or think that a PSU can be intermittently faulty, leading them to suspect the PSU despite evidence it works elsewhere.
✗The power button is faultyWrong answer — click to see why▾
Why this is wrong here
The technician measured 3.3V at the motherboard's power button header when pressed, which indicates the button is functioning correctly and sending the power-on signal to the motherboard.
★ When this WOULD be the correct answer
A desktop computer does not power on; pressing the power button yields no response, and a multimeter at the power button header shows 0V when the button is pressed, while the power supply passes a PSU tester. In this scenario, the power button is faulty.
Why candidates choose this
Candidates may assume that if the system doesn't power on, the power button is a likely culprit, especially when other components like the PSU test good, without verifying the button's signal with a multimeter.
✗The BIOS has become corruptedWrong answer — click to see why▾
Why this is wrong here
A corrupted BIOS would typically prevent the system from booting or cause POST errors, but it would not prevent the PSU fan from spinning or LEDs from lighting, as the motherboard still receives power and initializes. The symptom of no power at all points to a hardware failure, not a firmware issue.
★ When this WOULD be the correct answer
In a scenario where a computer powers on (fans spin, LEDs light) but fails to boot, displays a black screen, or beeps repeatedly, and the PSU and other hardware test fine, a corrupted BIOS could be the cause. For example, after a failed BIOS update or power outage during a flash.
Why candidates choose this
Candidates may associate power outages with BIOS corruption, as sudden power loss can interrupt BIOS updates. However, they overlook that a corrupted BIOS still allows basic power delivery and fan operation, unlike the total power failure described here.
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?”
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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.