PC Powers On Briefly Then Shuts Down: Missing CPU Power Connector
A technician is building a desktop PC. After installing the motherboard, CPU, and RAM, the technician attempts to power on the system. The fans spin for a second and then stop. The motherboard's power LED does not light up. The technician has confirmed the power supply is functional by testing with a multimeter. Which of the following is the MOST likely cause?
Quick Answer
The answer is the missing 4/8-pin CPU power connector. This is correct because the CPU requires its own dedicated 12-volt power rail from the power supply to initialize; without it, the motherboard may briefly send a start signal, spinning the fans for a second, but then immediately shut down as the CPU fails to communicate. On the CompTIA A+ Core 1 220-1101 exam, this scenario tests your understanding of power delivery stages—a common trap is to suspect a dead motherboard or faulty PSU, but since the technician confirmed the power supply is functional with a multimeter, the missing CPU power connector is the most likely cause when the PC powers on briefly then shuts down with no POST. Remember the memory tip: “No CPU power, no POST—fans spin once, then it’s toast.”
⚠ Common exam trap
CompTIA often tests the distinction between a system that fails to power on at all (front panel header issue) versus one that starts briefly and then stops (missing CPU power or short circuit), and candidates frequently confuse a dead CMOS battery with a power delivery failure.
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 4/8-pin CPU power connector is not connected.
The most likely cause is that the 4/8-pin CPU power connector is not connected. Without this dedicated power supply to the CPU, the motherboard may briefly attempt to start (fans spin for a second) but then immediately shut down because the CPU cannot initialize. The power supply is confirmed functional, and the motherboard's power LED not lighting up further indicates a missing critical power rail, not a dead CMOS or incorrect front panel wiring.
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 CMOS battery is dead.
Why it's wrong here
A dead CMOS battery can cause BIOS settings to reset but does not prevent the system from powering on. The system would still boot and display an error. It would not cause the power LED to remain off.
- ✓
The 4/8-pin CPU power connector is not connected.
Why this is correct
The CPU power connector (EPS12V) provides dedicated power to the CPU. Without it, the motherboard may begin to power on (fans start) but then immediately shut down because the CPU does not receive power. The 24-pin main power connector supplies power to the motherboard itself, but additional CPU power is required.
- ✗
The RAM is installed in the wrong slots.
Why it's wrong here
Incorrect RAM slot installation may cause no POST or beep codes, but the system typically does not shut down immediately; it stays powered on with no display. Also, the power LED usually lights up if the motherboard is receiving power.
- ✗
The front panel power switch headers are incorrectly connected.
Why it's wrong here
If the power switch headers are incorrectly connected, pressing the power button might not start the system at all. The scenario describes the system starts briefly, indicating the power button is working correctly.
Go deeper
Related to this question
Learn chapter
PSU Connector Types: 24-pin, PCIe, SATA
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.
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 →
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 technician is building a new desktop computer. After installing the motherboard, CPU, RAM, and graphics card, the technician connects the 24-pin main power cable and all other necessary cables. When the power button is pressed, the fans spin for about one second and then stop. The motherboard's power LED does not illuminate. The technician uses a multimeter and confirms the power supply outputs 12V, 5V, and 3.3V on the appropriate pins of the 24-pin connector. Which of the following is the MOST likely cause of the issue?
medium- A.The front panel power switch header is connected to the wrong pins.
- ✓ B.The 4/8-pin CPU power connector is not connected.
- C.The RAM modules are not fully seated in the slots.
- D.The CMOS battery is depleted and needs replacement.
Why B: The 4/8-pin CPU power connector provides dedicated 12V power to the CPU voltage regulator module (VRM). Without it, the CPU receives no power, so the system immediately shuts down after a brief fan spin (due to residual charge or a momentary power-on signal). The multimeter confirms the main 24-pin ATX connector is delivering correct voltages, ruling out a PSU failure.
Variation 2. A technician is building a new desktop computer. After installing the motherboard, CPU, heatsink, RAM, and power supply, the computer powers on for a few seconds and then shuts down immediately. The technician has checked all power connections and they are secure. What is the MOST likely cause?
easy- A.The CPU is not compatible with the motherboard.
- B.The RAM is not seated properly.
- ✓ C.The CPU cooler is not installed correctly or the thermal paste is absent.
- D.The power supply is defective.
Why C: The system powers on briefly and then shuts down, which is a classic symptom of thermal overload protection. If the CPU cooler is not installed correctly or thermal paste is missing, the CPU temperature skyrockets within seconds, triggering the motherboard's thermal protection circuit to shut down the system to prevent damage. This is the most likely cause given that all power connections are secure.
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.