I noticed this afternoon that my PC was idling at 170w when it's normally at about 120w. I ran folding@home to put a full load on the cpu and gpu and it was running at 280w, again about 50w more than usual. I recently changed the overclock to 3.9GHz up from the usual 3.2GHz, so I decided to reboot and reduce the clock back to 3.2GHz. It got to the Windows logo and froze, right when a few pixels of colour in the logo appeared. I rebooted and Windows suggested a startup repair, so I chose that and it wouldn't finish loading before freezing. So I took the overclock right off and still couldn't boot into Windows. I've tried running memtest 3.4 but it keeps freezing after a few minutes, apart from a blinking cursor.
Over the last few months, the PC has occaisionally frozen not long after booting up. The PSU is a Corsair HX520 bought in January 2007, and it's probably been running nearly a third of that total time with being on most of the day. I'm wondering if it's on its way out or if there's another problem I should be looking at.
Edit: I've just checked the voltages in the bios. +5v is 4.999 and +12v is 12.239 to 12.302. Is that 12v reading a long way off normal?