CPU LED Stays On After Windows Installer BSOD — Ryzen 5 5600 on MSI B550-A PRO

Understanding and Troubleshooting Post-Installation Boot Issues on AMD Ryzen 5 5600 with MSI B550-A PRO Motherboard

Introduction

Building a new PC offers exciting opportunities, but it can also present unexpected challenges. Recently, a user encountered a recurring issue where their system, powered by an AMD Ryzen 5 5600 CPU and MSI B550-A PRO motherboard, exhibited a persistent failure during Windows installation. Specifically, after a BSOD during the Windows installer, the system would restart and become unresponsive, with the CPU debug LED permanently lit and no further POST activity. In this article, we analyze the problem, explore potential causes, and suggest troubleshooting steps to resolve such post-installation boot failures.

System Overview

CPU: AMD Ryzen 5 5600
Motherboard: MSI B550-A PRO (BIOS updated via Flashback to latest version)
RAM: 2x8GB Patriot Viper DDR4 3600MHz (running at default 2133MHz, XMP disabled)
GPU: Gigabyte RX 6600 XT Gaming OC
Storage: Not specified

Key Observations and Symptoms

The system boots normally initially, with the CPU LED lighting briefly during POST.
POST completes successfully: VGA and Boot LEDs turn off.
Windows installation begins, but a BSOD occurs, prompting a restart.
After restart, the system gets stuck: the CPU debug LED remains lit, only the CPU fan spins, and no display output occurs.
Removing RAM triggers the RAM LED to light, confirming detection of missing memory.
BIOS properly detects CPU specifications, including core count and frequency.
The hardware setup appears intact: no bent CPU pins, thermal paste properly applied, PSU cables verified.
Changing RAM slots or removing GPU does not resolve the issue.

Analysis of Potential Causes

Memory-Related Stability Issues

The RAM runs at default 2133MHz voltage (~1.19V), which may be insufficient for stable operation under certain circumstances. While XMP profiles are disabled, the low voltage and frequency could contribute to POST failures or instability during system reboots after BSODs.

CPU Initialization and Warm Reboot Failures

The constant CPU debug LED after restart suggests the CPU is not completing its initialization during POST. This might be due to memory initialization failures or CPU-specific issues manifesting during warm reboot rather than cold boot.