Can't Start up Windows

Hello,

I was trying to replace my Windows XP Theme and I had made a Copy of MSStyles and had "patched" it and now it doesn't start up.
A minute ago I had chosen the option to continue even if there was a problem (to detect it) and this is what I got :

"STOP : C000021a {Fatal System Error}
The Windows Logon Process system terminated unexpectedly with a status of 0xc0000005 (0x00000000 0x00000000).
The system has been shut down."

I don't want to have to do a Full System Restore, but if I have too I will.

Thanks in Advance.