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Difficulty: MediumMotherboard, RAM, CPU, and Power Issues

A technician assembles a new desktop workstation. When the power button is pressed, the motherboard power LEDs illuminate and the cooling fans spin continuously, but the system fails to display video, produces no diagnostic beep codes, and does not complete the Power-On Self-Test (POST). The power supply unit has been verified to be functional and correctly connected to the main 24-pin ATX motherboard power socket. Which of the following is the most likely cause of this issue?

  1. The auxiliary 8-pin EPS12V power connector for the CPU is disconnected.Answer
  2. B
    The memory modules are populated in adjacent slots rather than alternating dual-channel configuration slots.
  3. C
    The operating system boot loader files on the primary solid-state drive are corrupted.
  4. D
    The graphics card driver installed in the operating system is corrupt or incompatible.

Answer

The auxiliary 8-pin EPS12V power connector for the CPU is disconnected.
The 8-pin EPS12V auxiliary connector supplies dedicated power directly to the CPU voltage regulator circuit. When the 24-pin main ATX connector is attached, chassis fans and status LEDs will turn on, but without EPS12V power, the CPU remains completely unpowered. Because the processor cannot execute motherboard firmware, POST cannot start, leading to a silent system with no video output or diagnostic beep codes.

Step-by-Step Solution

1
Evaluate symptom behavior during power-on.
The motherboard LEDs and fans receive power, but the computer fails to POST, displays no output, and emits no diagnostic beep codes.
This indicates that basic 12V/5V/3.3V power is reaching the motherboard peripherals, but the processor itself is not executing BIOS code.
2
Trace power delivery requirements for modern CPU architectures.
The main 24-pin ATX connector supplies power to motherboard chipsets, PCI slots, and fan headers, but the CPU relies on the separate 4-pin or 8-pin EPS12V connector.
If the EPS12V power cable is unattached, the CPU cannot power on, halting POST before diagnostic routines or display initialization can occur.

Key Concept

CPU Auxiliary Power Requirements and Early POST Diagnostics
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Topics

Motherboard, RAM, CPU, and Power Issues

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