Power Supply

The PSU (Power Supply Unit), as with everything else, can fail. The problem with a failing PSU is if it starts sending too much voltage to the motherboard or other devices, which can then fail as well!

We already discussed failing capacitors on the motherbord, but they are also present in power supplies. If your PSU is more than 20 years old, I would recommend replacing it - the sooner, the better.

"But," you say, how would replacing it with another old PSU help?" It won't, but replacing it with a new one will! Yes, todays ATX PSUs still work for older computers. Older motherboard usually has a 20-pin connector for power, while todays PSUs have 24 pins. More often than not, you can seperatre the 4 pins from the rest, ending up with a 20-pin plug that works.

If you have an AT-motherboard, you can get adapters from ATX to AT pretty cheap.Note that some of the cheaper ones do not provide -5V, so beware when buying. Some components, like Sound Blaster 2 and Pro Audio Spectrum 16, requires -5V to operate, 

PSUs of today comes with SATA power connectors, but luckily the voltages are still the same - and adapters from SATA to Molex and Berg can be found pretty cheap. Yes, the large, old power connectors you used for harddrives and optical drives back in the day are called Molex - the smaller ones for floppy drives are Berg connectors.