Symptoms
- A colored LED (often labeled CPU, DRAM, VGA, or BOOT) stays lit on the motherboard
- A two-digit debug display shows a code instead of completing POST
- System doesn't display anything on the monitor
- Error occurs consistently at the same stage every boot
Likely causes
- CommonThe lit LED's category isn't detected or seated correctly (CPU, RAM, GPU, or boot device)This is literally what these LEDs are designed to indicate.
- CommonComponent seating issue in whichever category is indicatedReseating the specific flagged component often resolves it.
- PossibleFaulty component in the flagged categoryIf reseating doesn't help, that specific part may need testing or replacement.
- PossibleOutdated BIOS not supporting the installed CPU or RAMEspecially relevant with newly released CPUs on existing motherboards.
What to do
- Note exactly which LED is lit or which code number is shown, then check the motherboard manual for what it means.
- If it points to CPU, reseat the CPU carefully or check that the cooler and its power aren't loose.
- If it points to DRAM, reseat the RAM sticks and try one stick at a time.
- If it points to VGA/GPU, reseat the graphics card and check its power connections.
- If it points to BOOT, check that a bootable drive is properly connected and recognized in BIOS.
- If the code suggests a BIOS compatibility issue with a new CPU, check if a BIOS update is needed (sometimes requiring an older supported CPU to apply it).
Tools and parts
- Motherboard manual
When to call a pro
If the debug code points to a component that still fails after reseating and testing, a technician can confirm the diagnosis and replace the right part instead of guessing.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.