POST (Power On Self Test)
The diagnostic routine your laptop runs every time it powers on. A POST failure means the laptop cannot complete startup — and it’s always a hardware fault, not a software problem.
- What It Is
- Signs of POST Failure
- Common Causes
- People Also Ask
POST is a firmware-level diagnostic that runs automatically every time a laptop is powered on. It checks that the CPU, RAM, storage, GPU, and other critical hardware are present and responding correctly before handing control to the operating system.
If any check fails, the laptop halts — it cannot load the OS. The result is a laptop that appears to power on (fans spin, keyboard lights up) but shows a black screen and never reaches Windows or macOS.
- Laptop powers on but shows a completely black screen — no manufacturer logo
- Beep codes on startup indicating which check failed
- Flashing LED indicators in a specific pattern
- Error message: “No bootable device”, “Memory error”, or similar
- Laptop powers on briefly then immediately shuts off
| Cause | What Fails POST Check |
|---|---|
| Failed RAM | Memory check |
| GPU failure | Graphics output check |
| Failed storage drive | Storage device check |
| Corrupted BIOS | Firmware integrity check |
| Liquid damage to board | Multiple checks simultaneously |
Can POST failure be fixed by reinstalling Windows?
No — POST failure occurs before the OS loads. It is entirely a hardware problem. Reinstalling Windows will have no effect.
How is POST failure diagnosed?
Technicians use beep codes, LED flash patterns, and diagnostic tools (POST code readers, multimeters, oscilloscopes) to identify which hardware check is failing.
Is a POST failure always serious?
Not necessarily — some have simple causes (loose RAM, disconnected storage) that are easily fixed. Others indicate more serious failures (GPU fault, liquid damage). Diagnosis determines severity.
My laptop turns on but won’t boot — is that a POST failure?
Possibly. If you see the manufacturer logo briefly before failing, the OS is likely the issue. If you see nothing at all from the moment of power-on, POST failure is more likely.
Free board-level diagnosis to find the exact cause. Component-level repair where possible.
