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Difficulty: MediumMotherboard, RAM, CPU, and Power Issues

A technician completes a motherboard replacement on a desktop computer. Upon pressing the power button, the system power LED turns on and internal cooling fans spin continuously at high speed, but no video output is displayed and the system does not produce any POST beep codes. The internal speaker is confirmed to be properly connected. Which of the following is the most likely cause of this issue?

  1. The 8-pin EPS12V CPU power connector is not plugged into the motherboard.Answer
  2. B
    The system RAM modules are populated in non-matching memory slots.
  3. C
    The boot drive has corrupted operating system system files.
  4. D
    The dedicated graphics card driver was disabled prior to motherboard replacement.

Answer

The 8-pin EPS12V CPU power connector is disconnected from the motherboard.
The 24-pin ATX cable supplies power to motherboard circuits, fans, and LEDs, but the CPU requires dedicated power via the 4/8-pin EPS12V connector. When the EPS12V connector is missing, the system turns on fans but cannot initialize the processor to run POST, leading to no video display and no diagnostic beeps.

Step-by-Step Solution

1
Analyze the observed symptoms
Fans run and LEDs light up (main 24-pin ATX connector provides standby and basic board power), but no POST beep codes or video output occur.
Indicates that power is reaching the motherboard chassis components, but core processing hardware is unable to execute code.
2
Evaluate hardware power architecture
Modern CPUs rely on a dedicated 4-pin or 8-pin EPS12V connection to power the CPU VRMs.
Without this dedicated power line, the CPU remains completely unpowered and cannot execute the BIOS/UEFI POST sequence.
3
Identify the primary corrective action
Connect the 8-pin EPS12V power cable from the power supply firmly into the top-left motherboard power connector.
Restores electrical power to the processor, allowing POST to proceed normally.

Key Concept

CPU Auxiliary Power Requirements during POST
Estimated Time:1m 15s
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Topics

Motherboard, RAM, CPU, and Power Issues

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