PC won’t boot consistently – PSU sometimes spins, sometimes dead. Need help diagnosing.

Diagnosing Intermittent PC Boot Failures: A Systematic Approach

Building a custom PC can be an exciting experience, but it often comes with its own set of troubleshooting challenges. One common issue faced by enthusiasts and professionals alike is inconsistent system startup, which can stem from various hardware or connection problems. In this guide, we will explore a scenario where a user reports intermittent power supply unit (PSU) behavior and provides details about their build. We’ll walk through potential causes and step-by-step diagnostic procedures to identify the root of the issue.

Overview of the Issue

System Description:

Components:
Mushkin 16 GB DDR4-3200 RAM
Sharkoon VK4 Rainbow case
GIGABYTE GP-UD1000GM PG5 1000W PSU
INNO3D GeForce RTX 3050 TWIN X2
GIGABYTE A520M DS3H V2 motherboard
AMD Ryzen 5 5500 CPU
Kingston NV3 1TB SSD

Symptoms:

PSU fan spins briefly during startup or upon unplug/replug, but often does not spin.
CPU fan sometimes spins.
Case fans connected via Molex do not spin.
Performing a paperclip test on the PSU does not initiate power.
Unplugging and reconnecting components yields inconsistent behavior.

The user is uncertain whether this points to a short circuit, a faulty PSU, or other issues, and is hesitant to RMA the PSU without further evidence.

Potential Causes and Diagnostic Steps

1. Assess Power Supply Functionality

The PSU is a critical component, and its inconsistent startup behavior suggests potential faults.

Paperclip Test:
Since the PSU’s fan does not spin during the paperclip test, it might indicate a defective PSU, or the motherboard might not be triggering the PSU properly.
Testing with a Known-Good PSU:
If available, replace the current PSU with a verified working unit. If the system boots reliably, the original PSU is likely faulty.
Hardware Compatibility Check:
Ensure that the PSU provides adequate wattage and correct connectors for your components.

2. Verify the Power Connections

Loose or faulty power connections can cause startup inconsistencies.