I am having a Dell Latitude C640. It came with Windows XP Pro SP2 on it. I had also installed all the latest updates on it. It is working fine. I was adding some theming utilities on the same and found that now the system freezes o the logon screen. There were some updates also. But after reboot I cannot see anything on the screen. The system freeze on welcome screen and after few minutes there is a blue screen error. The error is STOP C000021 Windows Logon System Process terminated unexpectedly with a status of 0xc0000005 (0x00000000 0x00000000). What should I do to fix the problem.