Why did my computer revert back to the factory settings?

Episode 970 (2:09:49)

Richard from Poway, CA

Richard logged in the other day, and the computer looked just like it did the day he bought it. He didn't do anything at all! Leo says that the computer most likely rebooted and may have automatically logged into another unused account. Leo says to hit Ctrl-Alt-Delete, choose 'logout', and then log in to his own account.