XP Pro SP2 install problem

[Guest]

Need help on how to approach this problem.
Have installed SP2 to 3 PC's - no problem.
Installed SP2 to my XP Pro - I regret the day.
Install seemed to work ok, but the reboot was locked in a do loop.
Could not get to the sign in point. Hard drive would power down.
Reboot F8, no auto reboot resulted in blue screen and error

STOP: c000021a {Fatal System Error}
The Windows Logon Process system process terminated unexpectedly with a
status of 0xc0000005 (0x00000000 0x0000000)
The system has been shutdown.

Reboot F8, Safe Mode, no workie
Reboot F8, Last Known Good Configuration, no workie
Reboot F8, VGA Mode, no workie

Ran Windiag, all memory sticks AOK.

Can access the recovery consule.
No ASR taken before SP2
System "backup" done before SP2, copied to HD on another PC.
SP2's backup of system files selected and done.

Q15669 - refers to cause of Service Pack failure. No recommendations as to
how to fix it.

What does the error status of 0xC0000005 mean? Could not find info relating
to the stop.

What is the next logical step to restoring my PC?
What is the next logical step to backing out SP2?

Thanks

 

[Jupiter Jones [MVP]]

James;
How to use the Automatic Recovery feature to recover your computer if
the Windows XP Service Pack 2 Setup program is not completed
successfully:
http://support.microsoft.com/?id=875355

Reboot tapping F8 each second.
Select "Last known good configuration" at the menu.
If that fails, reboot tapping F8 again this time choosing Safe Mode.
Then System Restore to Date/Time before issue started:
Start/All Programs/Accessories/System Tools/System Restore

Otherwise perform a Repair Installation:
http://www3.telus.net/dandemar/repaxp.htm

When you are ready for SP-2, follow the Service Pack Installation
Checklist:
http://www3.telus.net/dandemar/spackins.htm