Windows Hangs @ Startup

I searched around the forum and didn't find anything terribly similar to what is happening with the computer i'm working on right now. Here's the scenario:

Computer:
Dell Optiplex GX620
Intel Pentium 4 with HT
Windows XP Pro Service Pack 2
1 GB of RAM


Background:
The computer was brought in due to viruses/viri. The computer would not boot just throw a very odd blue screen with no description on the error itself. Took the HDD out of the computer, plugged it into my workstation, scanned it with Norton Anti-Virus, found over 10 viruses and deleted them. Plugged the HDD back into the computer and it booted to windows. Installed Ad-Aware and Registry Mechanic, then scanned the computer with Norton that is installed on the HDD. Found 3 more viruses. Scanned with Ad-Aware found over 2k infected files. Scanned with Registry Mechanic and fixed over 700 errors.

Situation:
Occasionally the computer will not get to the login screen, it hangs in various areas, whether it be Preparing Network Connections, Applying System Settings or it won't even get that far. And this only happens occasionally but enough to make me not want to give the computer back to the user. I've scanned the HDD with chkdsk and fixed the errors it found there. Any other suggestions would be greatly appreciated. Thanks!

 

Well here's the situation after the first program install and removal (following the guide):

The computer will not get to log on screen at all, and now I've got to repair the windows installation again. Not sure if that's a usual step in the guaranteed malware removal guide, but usually you don't have to repair windows. Correct me if I'm wrong...

 

Seeing as how attempting these steps has so far caused more damage than it has helped, at least before I could log in to windows now that isn't a possibility until the repair finishes, I doubt I'll go any further, and ask that anyone who has any ideas on the initial problem post them.

 

I respect the fact that Malware can cause this to occur, but I can not place my belief in that being the cause now. After numerous scan's and quarantines and more scans and finding nothing, I simply can not expect there to be anymore malware left on the computer. I'm going to take the HDD out of the unit and attach it to my machine and attempt to finish this RRMF guide and will let you know the results from there.

 

After 3 days of trying to get the system back to normal, and I'm not saying that the RRMF guide caused these problems to occur, I'm saying that the removal of the Malware did, the final verdict is a complete format with a re-install. With future issues on Malware I'll attempt to follow the guide again, and maybe it will work out better the next time...