The PC freezes or reboots suddenly
1. This could indicate a failing PSU that is not supplying power correctly to the motherboard. You may be able to get the PSU serviced but in most cases you will be better off getting a new power supply.
2. This could be due to overheating of the PSU or CPU: If the PSU is overheating, the metal cabinet may be hot to touch or you might get a shock. Shut off immediately. Check if the PSU fan is working, clean or replace the fan if not working or spinning very slowly. If it’s a faulty PSU you may be able to service it. If the PSU seems normal it might be due to an overheating CPU.
The PC powers on after the second or third try
The mostly likely problem is that the power_ok (or power_good) signal is sent before the power supply has stabilised. Get a better quality PSU. In modern PCs, the power switch is a logic device that tells the PSU to supply full power to the motherboard. The power_ok signal tells the motherboard that the power supply is available and stable. If the signal is sent too soon the motherboard does not recognize it and stays off to protect itself. This can happen in lowerquality PSUs. Booting more than once is not recommended, and you will be better off getting a better PSU.
The PC powers on but nothing happens after that (no beep)
1. This may be due to the addition of new hardware that is overtaxing the power supply. Remove the last hardware component installed and check again.
2. A defective hard disk or one that is not plugged in correctly: Check the power cable to the hard disk. Sometimes it may not be fully plugged in. Check the hard disk on another system.
The PC powers on, beeps and stops. No Power On SelfTest (POST) messages.
This may be a motherboard problem and not related to the PSU. Check the motherboard section of this site.
The PC powers on and runs POST but there is no display
This may be a display card problem and not related to the PSU. Check the display section of this site.
There is a squealing/whistling/whining noise when the PC starts
This could indicate either a problem with the fan, which has accumulated dirt over time, or one of the internal components of the PSU. Switch on the PC and listen carefully to confirm that it’s the PSU fan and not the CPU fan or the hard disk. Usually, the noise will stop once the fan picks up speed, and you can ignore it temporarily. It’s a good idea, however, to clean out the dirt around the PSU fan using a PC vacuum. This will increase the working life of the PSU fan as well as the PSU itself. If the fan stops working, the PSU will generate heat and cause more trouble. So a little prevention will save you a lot of headaches later.
If the sound is not from the fan but from within the PSU itself, then you may be able to service it. A PSU has no ‘user-serviceable’ parts, and it’s best left to a competent technician, although in most cases of component failure, you will have to replace the PSU.