|You problem c000021a error is from winlogon.exe crashing.If none of these work, you might have to reinstall windows and use backups to restore the files.|
I1.) Download the UBCD 4 Windows and if you have access to another server with the same OS, copy the file winlogon.exe to a flash drive, the file is located under C:\WINNT\System32\winlogon.exe. Boot to the UBCD, It will ask you what you want to boot to, use your arrow keys on your keyboard to highlight Ultimate Boot CD 4 Windows, press enter, and it will load a windows XP interface. If it asks you any questions about starting drivers, network is unneeded, and is it askes you about USB, press yes. You will need to insert the flash drive, and, go to my computer. Locate the flash drive, and, copy the winlogon.exe from the flash drive to C:\WINNT\System32. It may ask you if you want to replace an existing file, press yes. Now, restart the server and boot from the hard drive. If this fixes your problem, your are in luck, if not, follow these instructions.
2.) If you use a backup program that makes a bootable disk for recovering data, and you backed up the entire hard drive, try to use that. If your winlogon.exe file was deleted, this could recover it.
3.) If you use the backup program that comes with windows, and, you backed up the entire hard drive, you can repair windows be booting to your Windows 2000 server disk, when the screen comes up with the options, about 5 minutes after booting from the disk, hit "R" on your keyboard for repair, then, press "R" again for repair, (Yes, you hit "R" twice), Then Press "F" For fast. It will repair your system files install with windows, then, after the restart, it will go through as if you just installed windows. Once that is finished, it will restart. If that fixes your problem, install service pack 4 for windows 2000 & all updates.. The recovery process uninstalls all updated system files. This will not affect any of your files you created on your server, only the windows critical system files. If your system has an 8x or slower cd drive, I would recommend swapping the drive for a faster one long enough to do the repair.If you don't swap the drive, it will take forever to repair.