If your computer has automatically rebooted and has this in the eventlog:
The computer has rebooted from a bugcheck. The bugcheck was: (0x0000…). A dump was saved in: C:\Windows\MEMORY.DMP. Report Id: (GUID)
Then it’s most likely caused by a BSOD from a driver issue.
To troubleshoot this:
Click the Start Menu and type verifier, right click the Verifier program and click Run as Administrator;
Select Create custom settings (for code developers) and click Next;
Select everything except Randomized low resources simulation and DDI compliance checking;
Select Select driver names from a list and click Next;
Click the table heading called Provider to sort the list by manufacturer, then select everything that’s not Microsoft Corporation and click Finish;
Click OK to restart the computer;
The computer will then BSOD with details of which driver caused the error (this is the one to fix);
After the computer reboots, fix the driver that was reported in the previous step (perhaps it can be upgraded, downgraded or disabled?);
Don’t forget to turn the Verifier off by typing verifier /reset from an elevated command prompt (Run as Administrator)!
Alternatively you can troubleshoot the computer has rebooted from a bugcheck error by installing WinDbg (which is another Microsoft program) and loading in the MEMORY.DMP file specified in the error message. You can then read this to see what driver caused the issue.