Just like the title says. It doesn't matter whether or not I'm in the middle of running something, or the system is just running idle overnight while no one is on it. The system is randomly rebooting itself (or rather, it's like it's power cycling, like it just shuts off and reboots). I've ran virus scans, as well as adware and spy searches, come up with nothing. My initial thought is that the power supply is failing, but I wouldn't know how to confirm this. Where should I begin with troubleshooting this, and what might be the cause aside from the PSU?