Worth a look: http://support.microsoft.com/kb/112455
, technical info follows:0xC000021A: STATUS_SYSTEM_PROCESS_TERMINATED
This occurs when Windows switches into kernel mode and a user-mode subsystem, such as Winlogon or the Client Server Runtime Subsystem (CSRSS), is compromised. Security can no longer be guaranteed
. Because Win XP canít run without Winlogon or CSRSS, this is one of the few situations where the failure of a user-mode service can cause the system to stop responding. This Stop message also can occur as a result of malware infestation or when the computer is restarted after a system administrator has modified permissions so that the SYSTEM account no longer has adequate permissions to access system files and folders.
If the reason for the reinstall was malware...I would say that odds are that you are still infected. My suggestion would be to ask to have this thread moved to the Am I Infected forum. The problem with that is that you don't seem to be able to boot into Windows to do anything useful.
If you are sure...not just wishful...that it's not a malware situation, then I would suggest a repair install of XP.
Could also be some type of hardware problem, but that's just enumeration of the logical suspects possible. You haven't posted sufficient information for anyone to make that call, IMO.