Desktop Powers On for Two Seconds Then Shuts Down: Finding the Short Circuit
A technician is troubleshooting a desktop computer that powers on for about two seconds and then immediately shuts down. The case fans spin briefly, the CPU fan starts, then everything stops. The technician has tested the power supply with a multimeter and all voltages are within specification. The technician has also removed all add-on cards, disconnected all drives, and reseated the RAM and CPU power cables. The problem persists. Which of the following is the MOST likely cause?
Quick Answer
The two-second power-on-then-shutdown pattern described here is a specific and recognizable signature, distinct from a system that fails to power on at all or one that boots and then locks up later. Modern power supplies include short-circuit and overcurrent protection circuits designed to instantly cut power the moment they detect an electrical short, which is exactly what produces a very brief burst of fan spin followed by an immediate, total shutdown. The technician has already eliminated the most common suspects: the power supply's voltages test correctly, add-on cards and drives are disconnected, and RAM and CPU power cables have been reseated, which removes component failures and loose connections as the likely explanation. What remains is a physical fault causing unwanted contact between the motherboard and the case, most often from a standoff installed in a position with no matching mounting hole, a stray screw, or a pinched cable making contact with a solder point. This pattern is worth memorizing: an extremely brief power-on followed by immediate shutdown, especially right after a build or a case swap, points toward a short circuit rather than a component failure, and the fix is a careful physical inspection of standoffs and clearances rather than replacing parts.
⚠ Common exam trap
Many exam-takers assume a failing power supply when they see a brief power-on, but the question explicitly states the PSU voltages are good, forcing you to consider other causes like a short circuit that triggers protection.
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
✓
Short circuit in the case or motherboard
The symptom of powering on for about two seconds and then immediately shutting down is classic for a short circuit protection mechanism. When the power supply detects a short (e.g., from a standoff in the wrong hole, a loose screw, or a damaged motherboard trace), it triggers overcurrent protection (OCP) or short-circuit protection (SCP) and cuts power to prevent damage. Since the technician verified the power supply voltages are good and reseated all connections, the most likely remaining cause is a short circuit in the case or motherboard.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Faulty power button
Why it's wrong here
A stuck-closed power button would keep the system powered, not cut it after two seconds; a failing button usually prevents startup entirely or causes random shutdowns under movement. It is tempting because button faults do cause no-POST symptoms, and it would be the answer if the board never received a power-good signal at all.
- ✓
Short circuit in the case or motherboard
Why this is correct
With the PSU verified within specification and all peripherals removed, a short circuit between the motherboard and case causes immediate shutdown protection after brief fan spin. Standoff or mounting faults are the remaining likely cause.
- ✗
Failing CPU
Why it's wrong here
A failing CPU typically produces no POST, beep codes or thermal shutdown, but the stem already shows the PSU delivering correct voltages and the CPU fan spinning, so the shutdown is triggered by a protection circuit rather than the processor itself. CPU replacement would be correct only after confirming the board's VRM and thermal sensors are healthy.
- ✗
Incompatible RAM
Why it's wrong here
Incompatible RAM usually prevents POST or triggers repeated beep codes, and reseating it would not resolve a genuine mismatch; the described two-second shutdown points to the motherboard detecting an abnormal power-rail condition. RAM compatibility would be the answer if the system posted then failed memory training or threw a DRAM LED.
Go deeper
Related to this question
Learn chapter
Troubleshoot: Power and POST Failures
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).
Key term
RAM
RAM (Random-Access Memory) is volatile computer memory that temporarily stores data for quick access by the CPU.
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Same concept, more angles
2 more ways this is tested on 220-1101
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A desktop computer powers on for about two seconds (fans spin, LEDs flash) then immediately shuts down. It repeats this cycle if the power button is pressed again. The technician has already replaced the power supply with a known-good unit, removed and reseated all expansion cards and memory modules, and tested the system outside the case on a non-conductive surface. The problem persists. Which of the following is the MOST likely cause?
hard- ✓ A.The motherboard is faulty
- B.The CPU is faulty
- C.The RAM is incompatible
- D.The graphics card is drawing too much power
Why A: The symptom of powering on for about two seconds and then immediately shutting down, followed by a repeating cycle, is classic for a short circuit or a critical motherboard failure. Since the technician has already replaced the power supply with a known-good unit, reseated all components, and tested the system outside the case (eliminating case shorts), the only remaining component that can cause this exact behavior is the motherboard itself. A faulty motherboard can fail to initialize the CPU or power regulation (VRM) correctly, triggering the system's overcurrent or thermal protection within seconds.
Variation 2. A technician is troubleshooting a desktop computer that powers on for about one second and then shuts down. The technician has already removed all expansion cards and disconnected all drives. The system still exhibits the same behavior with only the CPU, motherboard, one RAM stick, and power supply connected. Which of the following is the MOST likely cause?
hard- A.A faulty CMOS battery.
- ✓ B.An incorrectly installed motherboard standoff causing a short circuit.
- C.Incompatible RAM speed.
- D.Overheating CPU due to improper thermal paste application.
Why B: The symptom of powering on for about one second and then shutting down, even with only the CPU, motherboard, one RAM stick, and power supply connected, strongly indicates a short circuit. An incorrectly installed motherboard standoff that contacts the motherboard's traces or solder points can create a direct short to ground, triggering the power supply's overcurrent protection (OCP) and causing an immediate shutdown. This behavior persists regardless of other components because the short is on the motherboard itself.
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.