Hi Whaton|y,
sometimes you pc will auto restart due to overheating of devices. This is to prevent the devices from getting burnt.
You could check your CPU temp. at BIOS or if you recently installed some new devices, supply the correct voltage to them at BIOS also.
Otherwise scanned you pc for virus/malware. These may cause irregular exception too.
If possible, right click "My Computer", select Manage
Navigate to Computer Management (Local)>System Tools>Event Viewer
Check the Application Log and System Log, jolt down the last few event before your pc restart and post it here, maybe we can help.
Lastly, backup your important files and format you pc. If problem presist after formatting, take your pc to service.
