Hi I've just bought a new PC and for the first week or so everything was fine and I loaded up all the software I needed and tweaked it just how I wanted it. The PC is a custom built job from CCL using a small Antec Cube case, an asus P5B micro ATX motherboard, core2duo processor and 2600XT graphics card. However now I've hit a problem. After several days of running with no problems the PC started shutting itself down and rebooting, but seems to stall at the motherboard post screen. Initially it would boot to windows ok but shut down again after a couple of minutes, but after a couple of times it wouldn't even do this and stuck at the post screen. I'm pretty sure the hard drive is ok, as it wont even boot with the XP disk. I've had an engineer out and he replaced the motherboard and it all booted up fine, however again after a few minutes it shut down and rebooted into windows. It did this a couple of times until eventually it again wouldn't get past the post screen. The engineer has taken it back to base to fix and I'm sure they will find the problem and fix it, but out of curiosity does anyone have any ideas what may be causing this? Many thanks.