Can you boot to safe mode with command prompt?
If you can, you can invoke Windows Restore to revert your computer to a date before this problem began.
To accomplish that:
1.Restart your computer, and then press F8 during the initial startup to start your computer in Safe Mode with a command prompt.
For additional information about the Safe mode with a command prompt, click the following article number to view the article in the Microsoft Knowledge Base:
) A description of the Safe mode boot options in Windows XP
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/