Glossary → Desktop PC Repair Terms
What Is POST?
The Power-On Self-Test your PC runs every time it starts.
Definition: POST (Power-On Self-Test) is a quick hardware check run by the BIOS the moment you power on. It confirms the processor, RAM and graphics are working before handing over to Windows. If something fails, the PC stops and signals the problem.
“Powers on but won’t POST”
This is the classic symptom: fans and lights come on, but the screen stays black and Windows never starts. It tells us the power supply is at least partly working, and points the search towards RAM, the GPU, the processor or the motherboard.
Beep codes and debug lights
Many motherboards report POST failures with a pattern of beeps or small labelled LEDs (CPU, DRAM, VGA, BOOT). Note which light stays on or count the beeps before you bring it in. It speeds up the diagnosis.
Common causes of POST failure
A RAM stick that has worked loose or failed, a graphics card not seated properly or missing its power cable, a bad BIOS update, or a motherboard fault.
Related terms
→ BIOS — the firmware that runs POST
→ CMOS Battery — resetting it can clear some POST problems
Fans spin but no display?
Free diagnosis to find which part is failing POST.