Your post reminds me how out of touch I have become with this kind of problem (and I am just posting about a possible win install too). However like you, I remember some things from my past and I suspect that your problem is probably a simple fix. At least for the time being, I think reinstalling windows is extreme and since you have a second working computer you should wait for some of these other clever folks to help. I'll bet there is some utility to help with this but if not, there must be a way to mnually link particular extensions to specific programs, and for the time being you would probably only need to make a couple of links (but don't ask me how).

If you are doing an "image" or "clone" backup, that will include the OS as well as all your installed programs, updates, and document (pictures, music, etc.). Then if the hard drive is indeed failing, you can purchase a new one, not expensive at all now, install it, and use the clone to reinstall your entire computer with everything just as it is right now. There are several free programs that will make this type of backup for you if you can get one to install. This will save you a ton of work bringing everything up to date since XP has been around long enough that there are a ton of updates. I have used this one and find the GUI very easy to follow: Here is a link that might be useful: EASEUS ToDo Backup Free

you said you got a virus and know that is the problem, well that is not up to Dell support to fix, under any circumstance. Their support is for their product (they do provide online guides and manuals for each pc have you looked for yours), they are not there for assistance in removing infection. If you had a part that failed on the computer then they should help with that but something that is being caused by a virus that you got by doing something is not Dell's fault. Now I am NOT a Dell fan, I personally would not buy one. But any PC manufacturer certainly has the right to say no to that type of situation. If they have helped before they went way beyond the scope of their support requirements. I do own ACER and HP and would not consider calling either of them for help if I had an infection. This is why you should go to the free forum I listed and ask for help to clean your machine. Run a malwarebytes free scan How to download and install Malwarebytes' Anti-Malware application for Windows computers which may fix this problem. Go to an online AV and do a free scan there also ESET Online Scanner What antivirus is on your pc? is it fully updated and does it run weekly scans? what other antimalware scans do you run? Have you run the secunia tool to make sure everything is fully updated on the pc to help prevent any infections through out dated programs like adobe, java and flash? Secunia Online Software Inspector (OSI) Let us know what you need assistance with and we can try to help you get it done.

"F2 for setup and F12 for boot options." Are you saying you get this far and the computer REBOOTS by itself, if that is the case you start to consider a power issue here. How many files did the user want to save? Where are the 2 recovery disks that should have came with the pc, or does it have a recovery partition that you would have an option for after hitting F12 if you get that far. If you slave the drive run your options scan disk, check disk ect, the go to the manfactures site of the hard drive an run there tests on the drive. I wonder if you can get recovery disks from Dell for the 2400 series?