A few weeks ago, my son's computer caught fire and melted the HDD. We were able to save everything (we think). So last night, my son and I rebuilt my computer yesterday into a new case, and everything was working smoothly. After using it for a couple of hours, though, it shut off on its own. After rebooting it, it did the same thing after a few minutes. After starting it from this point, it would remain powered on for about 2 seconds before turning off before cycling and repeating the process on its own. After waiting overnight, it's currently working (I'm typing this post on it right now and going on 30 minutes) While building it, I discovered that I had an issue with a bad stick of RAM that gave me the same result, but that doesn't seem to be the issue again. I tried booting it without any drives or RAM in and also without my graphics card, but it had the same issue. Again, everything seems to be working now, so I'm not sure why it shut down before.