Troubleshoot POST Issues
Once the CPU has been given the power good signal, the system firmware performs a power-on self-test (POST).
- POST is a diagnostic program implemented in the system firmware that checks the hardware to ensure the components required to boot the PC are present and functioning correctly
Info
- On modern computers the POST happens very quickly to improve boot times, so you are unlikely to see any POST messages
- Also, the PC is likely to be configured to show a logo screen and will only display messages under error conditions
- If power is present—you can hear the fans spinning, for instance—but the computer does not start, there is a black screen, and there are no beeps from the internal speaker, it is likely either that the display is faulty or that the POST procedure is not executing
- after ruling out issue with the display, you can troubleshoot POST
POST Troubleshooting Steps
- Ask what has changed
- If the system firmware has been updated and the PC has not booted since, the system firmware update may have failed
- Use the reset procedure
- Check cabling and connections
- incorrectly oriented storage adapter cable or a badly seated adapter card can stop the POST from running
- Correct any errors, reseat adapter cards, and then reboot the PC
- Check for faulty interfaces and devices
- possible that a faulty adapter card or device is halting the POST
- Try removing one device at a time to see if this solves the problem
- or remove all non-essential devices, then add them back one by one
- Check the PSU
- Even though the fans are receiving power, there may be a fault that is preventing the power good signal from being sent to the CPU, preventing POST
- Check for a faulty CPU or system firmware
- If possible, replace the CPU chip with a known good one or update the system firmware
Info
- Some motherboards have jumpers to configure modes (such as firmware recovery) or processor settings
- If the jumpers are set incorrectly, it could cause the computer not to boot
- If a computer will not work after being serviced, check that the jumpers have not been changed
- If POST runs but detects a problem, it generates an error message
- As the fault may prevent the computer from displaying anything on the screen, the error is often indicated by a beep code
- Use resources such as the manufacturer’s website to determine the meaning of the beep code
Codes for the original IBM PC:
| Code | Meaning |
|---|---|
| 1 short beep | Normal POST, system is OK. Most modern PCs are configured to boot silently, however. |
| 2 short beeps | POST error, error code shown on screen. |
| No beep | Power supply, motherboard problem, or faulty onboard speaker. |
| Continuous beep | Problem with system memory modules or memory controller. |
| Repeating short beeps | Power supply fault or motherboard problem. |
| 1 long, 1 short beep | Motherboard problem. |
| 1 long, 2 or 3 short beeps | Video adapter error. |
| 3 long beeps | Keyboard issue (check that a key is not depressed). |
Info
- Some PCs will not boot if a key is stuck
- Check that nothing is resting on the keyboard
- if the board is clogged with dust or sticky liquid, clean it using approved products, such as swabs and compressed air blowers