Ya, like nascar said.
And if by any chance you don't have a second drive to use. Don't forget all you really need is to install the O/s and Anti Virus, so any old small cheap drive should do long as it's big enough to install the basics. Might even be able to borrow one. You should be able to find out if you got a virus, fix it, or if something else fix that too.
Install New small drive as master only, setup O/s and anti virus, install your old drive as slave, then use small master drive to boot and scan your big drive you got now. I think that should work.
I mention that because around here most the people I know with systems have only one drive, and not easy to borrow an 80gig or larger
I've got old drives I can use this way and for loaning out, 850meg, 250meg, 1 gig, and 2 gig.
Not worth selling them, so I keep em for loaners
Also if you know what all your missing files are, depending on what they are, you can probably copy them from the smaller drive over to the drive you have now if you know where they go. I have done that before when something has gotten trashed. Like a problem I had starting a system, it would boot to the windows logo then tell me safe to shut down! Finnaly I found the bad files causing it, copied them to floppie from another system and overwrote the bad files with them. Fixed it!
SO if you don't have a second drive and can't buy a good one, look for a working small spare free or cheap
Also I think I saw you had screen problems at yahoo in another post? I have several yahoo acounts in this family of 3, my main box has been acting wierd also but none of the others do and that is using different systems to access it also. I think it's a Yahoo thing? First go to check mail, and nothing on the left side where folders and such should be, just mail heading across the full width of the screen. Corrects itself after I read or delete the first time and the page refreshes.