As you say it might be a motherboard or other hardware problem and if it is, I'm not clever enough to help you there.
But something struck me. You said she is not on the internet , but you found 11 instances of the Sasser b (or whatever) virus.
If she's not on the internet but her computer had viruses, they must be coming from somewhere, eg infected floppy disks or CD's.
Therefore, when you cleaned her system and returned it to her, did she then re-infect the computer from those same disks?
If so, perhaps those same viruses are slowing her system down again.
Just a thought.
Sorry for the long post, I'm at witt's end here.
My cousin's computer has gone haywire after the warranty expired (of course). I've been tyring to help her get it going again but it seems each time I fix something and return the machine to her -- a new problem crops up. She does not want to reformat the HDD at this time -- although that is about my last solution. I think there is a hardware problem because I pulled out her HDD and tried one of mine with Xp Pro just pulled from a working machine and it would not boot properly either...
At first computer would not boot. Keep flashing error message : windows\system32\config\system file missing and then trying to reboot. She could not find her restore disks at this time. Based on research in various forums, I advised her that she needed to find her restore disks and that she may want to replace memory and/or motherboard. She decided to buy a second stick of 256MB ram. While waiting for this to arrive (bought from Crucial) she used a friend's restore disk (from a Dell) and got her computer booting again. She still wanted me to install ram.
As she lives off her cell phone and does not have internet, I bought tower home with me and installed ram. System booted fine for about an hour and then started slow time warp problem where you click on something and it shows up 10 minutes later. It did not do this in safe mode - so I ran an anti-virus check and found 11 instances of Sasser b (I believe). I ran Maxtor's Powermax to test HDD, fine. I installed Norton systemworks 2003, Adaware Se home, and Spybot (I run both on all my machines), Scanned for everything. Installed all Windows and Antivirus updates. Machine running fine, fast and happy. Send machine home. Thought I was done with it.
She calls again. Computer is in slow time warp, this time even in safe mode. She still does not want to reformat HDD. I'm going over there today to see. I still have the feeling this is a hardware problem, either motherboard or memory. From what I seen on various forums this particular machine is not good, lots of folks seem to have problems with it and when they replace the motherboard the problems go away. I've pulled all of the startup programs like Office but I will check msconfig -- If I can get into it. I will also try running it on just the new ram -- any other ideas would be greatly appreciated...
Celeron 2.0 GHz
400 MHz Front side
Motherboard Trigem Glendale chipset: 845GL
2 sticks 256MB DDR Pc2100