Just at thought:
I haven't seen this mentioned, but here's something to try if there seems to be a virus imbedded in the computer and anti-virus software isn't taking care of it.
Go to "Start," then "Run." Type in "msconfig" (w/out the quotes). Click on the "Start Up" tab. At the same time, on another computer nearby, or if possible, the same computer, go
here. In the search box at that site, type in the command or data you see in the (infected computer's) Start Up list that looks suspicious. There's a key that tells you if it's a virus or not. After you uncheck any boxes that show a virus, click "apply," and leave it in "Selective Start-up." I did this with my ancient Windows ME and it's still (fingers crossed ) running. I've also done this on two other computers, too, and it's fine.
I did this with my son's computer when nothing--not up-to-date anti-virus software, Spybot, Ad-aware, etc,--worked. What I did above, finally did the trick.