The STOP 0xC000021A error occurs when either Winlogon.exe or Csrss.exe fails. When the Windows NT kernel detects that either of these processes has stopped, it stops the system and raises the STOP 0xC000021A error. This error may have several causes. Among them are the following:
Mismatched system files have been installed.
A Service Pack installation has failed.
A backup program that is used to restore a hard disk did not correctly restore files that may have been in use.
An incompatible third-party program has been installed.
Probably the easist method to fix this is byt using the last known good configuration.
To start the computer by using the last known good configuration, follow these steps:Note Because there are several versions of Microsoft Windows, the following steps may be different on your computer. If they are, see your product documentation to complete these steps.
1. Click Start, and then click Shut Down.
2. Click Restart, and then click OK.
3. Press F8 at the indicated time:
For an x86-based computer: When a screen of text appears and then disappears , press F8. (The screen of text may include a memory test, lines about the BIOS, and other lines.) There may also be a prompt that tells you when to press F8.
4. Use the arrow keys to select Last Known Good Configuration, and then press ENTER.
NUM LOCK must be off before the arrow keys on the numeric keypad will function.
5. Use the arrow keys to highlight an operating system, and then press ENTER.
Choosing the Last Known Good Configuration startup option provides a way to recover from problems such as a newly added driver that may be incorrect for your hardware. However, it does not solve problems that are caused by corrupted or missing drivers or files.
When you choose the Last Known Good Configuration option, only the information in registry key HKLM\System\CurrentControlSet is restored. Any changes you have made in other registry keys remain.
I would also look in your event viewer to see what errors you have there, and post them here.
Edited by SRX660, 30 July 2008 - 11:27 AM.