OK, I built a computer for my parents two days ago running a h67 mobo with an i3 2100, 4GB of ram, on board graphics and a 300 watt psu. After installing windows 7 64 bit there was no problem but today dad turned on PC to find it constantly restarting itself. There is is no video signal either and the keyboard lights don't flash and the mouse doesn't light up. Never had any problems like this with my gaming rig... Any help would be greatly appreciated.

Reseat the memory modules, test or swap the power supply, and check for any loose screws or other items left in the case. Also check if the reset button on the case got jammed, sometimes it's the low tech things.

First, with the PC off course, and the AC plug removed, try re-seating all your cards including ram. Then clear your cmos by taking the battery out for about 20 seconds, put it back in and reboot.