Troubleshooting: PC keeps restarting over and over again. Can you help me get it to stop?

I have an Asus U56E laptop running Windows 7.

Earlier today, it started to randomly restart on its own, over and over again. No error messages, no obvious problems. I figured it might be a virus, so I tried running Symantec Antivirus, but the computer restarts on its own every few minutes, so it’s not possible to finish the scan.

I also tried going into Advanced Boot Options and selecting selecting “Disable automatic restart on system failure.” That didn’t work either.

I restarted in Safe Mode, and the computer seems stable (so far so good), but I’m not sure what to do from here. I don’t have a copy of Windows 7, so re-installing the OS or anything like that isn’t an option. Any suggestions?