Windows XP won't start up: Fatal System Error Message

My sister's Dell desktop got the New Win31 virus(?) recently and I told her to try follow the Read and Run Me on the forum. She started to go through the steps, but after she did the Msconfig and rebooted, she couldn't log back in to her account. It went to a window that asked for a login name and password, which we don't have because we never put passwords for our separate accounts.

So now, we try to search on how to bypass that window and login somehow, and read on another site to try Safe Mode. Unfortunately, now we're getting a blue screen saying,

"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."

I've tried the F8 at start up and going under Last known good configuration, but it doesn't help. So now we're stuck with the computer starting up and just going straight to the blue screen. Is there something that we can't do to fix it? We don't have the CD for XP, so I can't repair her computer using that either.

I'm at a lost and my sister doesn't know anything about computers, so any sort of help would be much appreciated. Thanks in advance.