"...windows has been shut down..."after malware removal. Help!

I am trying to clean my mother-in-law's computer of viruses, malware, etc. She has no antivirus program, firewall, etc, running. I found and removed cyber security using Superantispyware. The next day I installed Avast antivirus and ran that scan at the same time as a second SAS scan was running. Avast found a virus but when I tried to quarenteen or remove it, the program would say that it could not remove the virus because the file could not be found. I have no idea what file it is talking about. It does however keep popping up with the virus warning, but always the same results. The SAS scan froze. When I restart the computer get a blue screen that says "A problem has been detected and Windows has been shut down..." I restarted the computer many times and get this same message when trying to start in safe mode, last known good configuration, and start windows normally. So, now that is as far as the computer goes. Cannot get past the blue shut down screen. I could really use help as she is counting on me to fix this!!!

Dell desktop (old one)
Windows XP

 

I will give that a try and follow up. Thanks!

 

I am trying to "How to recover from a corrupt registry" and am getting stuck in step one. I typed in all the information under copy, then all the info under delete, then hit a problem. When type in copy c:\windows\repair\system c:\windows\system32\config\system, it tells me it cannot find the file. I just ran chkdsk c: /r. Not sure what it did. When finished it just says total disk space, available space, 4096 bytes in each allocation unit, how many allocation units on disk and how many available. Not sure how to interpret this?? exited and restarted and got same message of file missing. Now what??:cry