Recover from winlogon failure

Ok, I got this blue screen error when booting my Dell/XP Professional computer after a shutdown with error with message:

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

There is no way to log in no matter what I do: not in safe mode, not in previous good configuration, not using the original XP Professional installation disk from Dell.

A good suggestion I received after searching on line is here.

It says my c:\windows\system32\winlogon.exe file is corrupted and I need to replace it with a good one.

Since I was not able to get in the system even with the original Dell installation CD, I tried to use Hiren's BootCD and it worked! I was able to back up my important files on C drive now.

I followed instruction by replacing c:\windows\system32\winlogon.exe with c:\windows\system32\dllcache\winlogon.exe, but it got the same error. I searched my computer and found C:\WINDOWS\SoftwareDistribution\Download\9866fb57abdc0ea2f5d4e132d055ba4e\winlogon.exe, then used this for replacement. It worked and now I can log in!

But I still see nothing after logging in, which means c:\windows\explorer.exe is also corrupted. Again, replace it with c:\windows\system32\dllcache\winlogon.exe did not work, but C:\WINDOWS\SoftwareDistribution\Download\9866fb57abdc0ea2f5d4e132d055ba4e\explorer.exe worked!

So now, one day later, my computer is recovered. I'm glad I didn't have to reinstall it.