PC won’t boot – no signal, no POST, blinking LED on motherboard – need help troubleshooting

Understanding and Troubleshooting a Non-Booting PC: A Guide to Resolving No Signal, No POST, and Motherboard LED Indicators

Introduction

A reliable personal computer is an essential tool for work, entertainment, and productivity. However, even the most stable systems can encounter unexpected issues, leaving users puzzled and seeking solutions. This guide aims to help users troubleshoot and resolve common boot-related problems, specifically when a PC exhibits no display signal, fails to POST (Power-On Self-Test), and shows a blinking LED on the motherboard. We will examine typical symptoms, potential causes, and step-by-step troubleshooting procedures, using a sample system configuration—an AMD Ryzen 5 3500X CPU paired with an ASUS Prime B450M-A II motherboard—as a case study.

System Overview

Sample Build Specifications:

CPU: AMD Ryzen 5 3500X
Motherboard: ASUS Prime B450M-A II
Memory: 16GB DDR4-3200 (2x8GB, tested individually)
Graphics Card: NVIDIA GeForce RTX 3070 8GB
Storage: 1TB M.2 NVMe SSD
Power Supply: Be Quiet System Power B9 600W (BN209)
Usage Duration: Over 5 years of stable operation with no recent hardware changes

Symptoms and Initial Observations

Without prior warning, the system refuses to boot properly, displaying the following behaviors:

CPU cooling fan spins slowly and continuously
GPU fans briefly spin up then stop
Motherboard’s orange LED pulses slowly, indicating standby or standby-like state
No video output, POST beeps, or BIOS screen
The system appears to power on but remains in a limbo state, not completing the POST or reaching the BIOS

Understanding these symptoms helps narrow down potential causes, which commonly include power supply issues, motherboard faults, CPU failures, or peripheral/interconnection problems.

Key Troubleshooting Steps

Assess Power and Initial Hardware Checks
- Verify Power Supply Functionality:
  Confirm that the PSU is supplying power not only to the motherboard’s standby circuit but also to the main rails. Subtle issues may cause insufficient power, affecting boot behavior.
- Inspect Physical Connections:
  Ensure all power cables (24-pin motherboard, 8-pin CPU) are securely connected. Check for any damaged or loose cables.
- Check for Visible Damage: