STOP C000021 - Windows Logon System Process terminated unexpectedly

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.

Go in event viewer and see what you can find. In event viewer you can find more detail on the error. Bluescreen mostly appear due to critical system file error or due to any hardware issue. You can try to run system restore or boot in safe mode and get rid of any latest updates installed. I think that will make your system more stable. If still bluescreen is constant then you have to re-install windows there will be no other way.

Run a repair installation. It happened to me also last month. Due to improper updates my system crashed due to bluescreen. I tried a number of solution but nothing worked. Then at the end I used windows installation disc and performed a repair setup which worked. There was not issue with the same. It is working fine now. Try to install updates manually. Do not just install anything. That creates serious issue later on.