Windows XP repair black screen

Working on a friend's computer. Dell told him to do a repair, that way he could keep his files, but hopefully repair the windows system files. After windows copies over the files and the computer restarts, windows logo loads and the screen goes black with the mouse cursor. It stops there and doesn't go any further. It's supposed to continue the install repair, but it's not getting there.

I did do a chkdsk r c: in the repair console and that went for hours and ended up still not doing anything. I put the hard drive into another computer and did a virus scan, removing upwards of 60 virus infections.

If this was my computer, I'd back up the files and format it and do a fresh install of windows. Unfortunately that's not the route that is preferred by the owner.

Any ideas?