Something very strange has started happening to my PC recently. For some unknown reason at completely random times, for example when clicking a hyperlink or when changing window, the computer just turns off. Then the front power button won't turn it back on again. You can hear the computer still power adapter wearing away so there hasn't been a power cut or any loss of external power. Once you turn the computer off by the rear power button it will then switch back on and be fine once you turn it back on.

I have Windows XP Media Centre on a Intel Pentium 4 PC.

Does anyone have any ideas?