[HELP] PC was working yesterday — now no display, VGA light on, even after BIOS Flashback and 2 GPUs

Understanding and Troubleshooting PC Display and Boot Issues: A Case Study

Introduction

Building a new PC can be an exciting experience, but it often comes with unforeseen troubleshooting challenges. Recently, a self-assembled system experienced a sudden loss of display output and persistent VGA debug indicator lights, despite initial successful startup. This article explores the problem in detail and provides a structured guide for diagnosing similar issues.

Case Overview

System Specifications

• Processor: AMD Ryzen 5 5600X
• Graphics Card: Gigabyte RTX 3060 Ti
• Motherboard: MSI B450M Mortar Max
• Memory: 2 x 16GB DDR4 RAM
• Power Supply: 650W (Brand unspecified)
• Storage: 1TB SSD
• Monitor: Confirmed functional

Initial Condition

The system was operational the day before, booting into BIOS with normal fan operation and display output. However, upon booting the following day, the system exhibited the following symptoms:

• No display signal on monitor (tested via HDMI and DisplayPort)
• VGA debug LED remains solid
• GPU fans are not spinning, though RGB lighting is active
• Monitor reports “no signal”

Troubleshooting Steps Attempted

The user conducted several standard troubleshooting procedures:

1. Reseated Components: GPU and RAM modules were reinstalled to ensure proper seating.
2. Memory Swap: Tried individual RAM sticks and different slots (e.g., A2) to identify faulty modules.
3. CMOS Reset: Removed the motherboard battery for one minute to clear BIOS settings.
4. Power Verification: Confirmed all power cables are correctly connected to GPU and motherboard.
5. GPU Swap: Replaced the primary GPU with a known working AMD RX 570; fans spun up, but display remained absent, and VGA status persisted.
6. Cable and Monitor Swap: Used different display cables and monitors to eliminate peripheral issues.
7. BIOS Update via Flashback: Performed BIOS flashing with MSI’s BIOS Flashback feature; indications suggest successful update.
8. Speaker Beeps: No beep codes detected, and motherboard does not indicate DRAM or CPU errors via LED indicators.

Current Status and Observations

• Both graphics cards do not produce display output
• GPU fans are inactive, but RGB lighting is present
• The VGA debug LED remains continuously lit
• The system was functioning perfectly the day before

Potential Causes and Diagnostic Strategies

Given the symptoms and