I'm having issues with my i3-530 H57 machine, which has been perfectly stable for a year, suddenly starting to randomly reboot. These aren't software/OS issues or BSODs, but instant power-offs and then auto-restarts 30 seconds or so later. Temps and cooling are fine, there have been no hardware changes except a discreet GPU added, but removing it hasn't solved the problem. PSU is a Corsair HX750, board is a GigaByte H57M-USB3. I suspect one or the other but I'm not sure which is more likely. Obviously I'm not particularly keen on attempting a mainboard change with Ivy Bridge around the corner unless it's absolutely necessary...

If anyone recognises this behaviour and can point me more certainly to the problem, I'd be very grateful.