Does the rebooting happened recently or did it just happened
today? If it has been happening for the last few days, scan for
viruses. Also check that the temperature is not too high. Anything
above 50 degrees might cause problems. If it happened just today,
check that computer temperature is not too high.
If temperature is not the cause, try this:
Open My Computer. Go to Tools, Folder Options.
Select the View tab. In the Advanced Settings, select the Show
Hidden files option. Try going to these folders and find those
files and delete.