Use Windows System Restore to revert your computer's system state to a date existing before the problem began.
1.Restart your computer, and then press F8 during the initial startup to start your computer in Safe Mode with a command prompt.
2.Log on to your computer with an administrator account or with an account that has administrator credentials.
3.Type the following command at a command prompt, and then press ENTER:
4.Follow the instructions that appear on the screen to restore your computer to an earlier state.http://support.microsoft.com/kb/304449/