Are you using the default cleaning options?
What did you do before the problem occurs (cleaning, changing settings, wiping free space etc)?
Method to recover: In Windows 7, you can try to use the System Restore to restore/recover your computer back to the last restore point which was created before the problem happens. However, this doesn't always work, but it's the best shot you'll have.
Anyway, this certainly sounds like the work of a virus. Try to scan for virus with your antivirus if possible.