It could be a faulty capacitor somewhere also. Try letting your PC run non-stop for 2 days and see if it acts up. After prolong discharge of the capacitor it works again.
OK. I will leave it on this whole weekend... Hopefully my daughter, Hui En does not pester me to switch it OFF. She likes to make sure that the lights, fans, etc are off before sleeping. The CPU has a light which will alert her that the PC is ON. Will have to tape the light.

We'll see how the PC behaves after this weekend. Thanks for the suggestion, Victor.