Hopefully it was only a bios conflit, if so you are very lucky.
*Just a bit of information.
The cause is usually as squirrelnmoose has said, a memory issue with OS specific data being corrupted, leaving the OS unsure what to do, thus is resets.
Motherboards can do this as well, a short in the board can send the kill signal, which would restart the computer as well.
Heating can be an issue, but more so in laptops, as long as the heatsink is still running properly that is not often a problem in desktops, there would be other signs before now if the case was becoming too warm.