Last night my PC was constantly turning on and off every few seconds.
Done a search and points to maybe a PSU prob but it could be anything
http://pcsupport.about.com/od/findbysymptom/ht/pconthenoff.htm
I was going to try the PSU from my old PC but it was an old one (prob AT from searching google)
Because old PSU would not fit I reconnected the original one back up and all is now working fine
Very strange as I did not change anything
I will leave it whilst it is still working but any ideas why this may happen?

Computer virus, perhaps?

Either that or your computer is haunted!

http://paranormalis.com/threads/haunted-computer.5564/

Its overheating.
The heat sink may have come loose.
If you keep trying it you could cause permanent damage. Open it up and check.

lol YingYang, it aint that
Hi Mark
Do you mean if I ignore it and just keep booting up without checking?

Open it up and see if the heat sink is loose on the motherboard, as Mark said. If you dont know what to look for, you could try a computer shop.

The heatsink is solid
The pc is only a year old

If its working ok now. then it could have been a loose connection.

You Pc Vibrates and anything is possible.

If was shutting down quickly after a cold start up then its more than likely a thermal even (Getting too Hot).
So each time you tried to re-boot the pc it would still carry over that heat and a thermal event would happen a bit quicker.

Processors need to be cooled. A motherboard can detect over heating and shut it all down to prevent permanent damage. Or kill the pc, no soft shut down just OFF !

And the same situation can result in a loose wire its connected or its not.

If its running ok now after you plugged the leads back it, that's great disaster over.

Repeated Thermal Events can dry out the contact pate between your processor and heat sink. Which makes the paste useless.

Hope that helps.

My HP does it every so often, there's an issue with the memory slots (same with some Dells too), and if I take out the RAM, give the slots a clean with compressed air that sorts it.

I think its known as "chip creep".

It was probably a loose wire as all is still ok
If it happens again think I will check the contact paste
Cheers Mark