When you attempt to boot your target system, a blue screen is displayed with the message "c000021a".
The most common cause of this error is a missing device driver dependency. This can occur even if the device driver is not critical for the system to boot. For example, Redbook.sys is not required to boot the system. But if one of its dependencies, Ks.sys, is not included in the run-time image, the system displays the error code 0xc000021a.
1. Identify missing dependencies. For information, see Checking Dependencies in Windows XP Embedded Studio Help.
2. If you determine that a dependency is not missing, then the error probably occurred because a file that the driver depends on is missing. Use the Microsoft® Visual Studio® Depends utility, which runs using the Depends.exe file, to view the statically loaded libraries. The libraries are located in the import section of the binary file. Search for required files that are missing from your run-time image.
Have you tried hitting the F8 key while your computer is booting up and then going to the LAST KNOWN GOOD CONFIGURATION?
If that does not work you will probably need to do a repair install with a Microsoft CD.
The last choice is to pull the hard drive out and stick it in another computer to get any Data you want to save off the drive. You will need to take ownership of the folders and files on the drive, which is a PITA, to access the files.http://support.microsoft.com/kb/308421