Your original post was about repairing the PC, not saving files. I take it now you need to format in order to get back to a stable PC again. Besides all the fixes, if none of them work and you can't do a repair, you're stuck. Try to boot into safemode with networking after hitting F8 during boot-up. Once in safemode, try to save any files to a flash drive or ext. USB HD. Otherwise. its going to get hosed as time goes on, which if you hadn't already run your current AV pgm. to see if any virus, malware or trojans are present. Take action if any found and hopefully return to a stable system. But, if after 10yrs. you never did any progressive cleaning or maintenance, it maybe too late or one heck of a job to recover. Your complaint is not uncommon for an older PC or unkept one, so it becomes harder to resolve, which the easiest way to become stable again to reformat and reload OS, drivers, updates etc.,. Critical files should have been kept now and then on some time table in order to reduce this headache.
If not already, and XP own restore feature was active, use a restore point before the troubles began. -OR- as already explained get your hands on a XP repair disc, this NOT a restore/recovery disc but it does fix OS issues and such. Vendors offer them online, some are free(trusted source???) but many for small cost. Access to an XP install disc which is recovery/restore see if the repair console is present and use it. Google for hints and tips to explain usage.