Ya sure windows is fixable, If you know what you are doing, but most of the time is just a waste of time... once one part goes out it creates to many instabilities... hell if you have to do a hardboot 3 or 4 times in a row do to a bad driver or IE gone haywire, then you've probably corrupted another hunk of windows do the HD abuse, so that as soon as you fix a problem, the likelyhood of having to do another frustration-born series of hardboots is just down the road....
The best thing to do when dealing with this is just not to install any extra software. XP will last a long time just as long as don't realy use it for much.. Becuase if you use it for something that the MS marketing didn't think off, or install a bunch of software on it then it's just your fault anyways for windows crashing all the time...
Also don't think that MS will every actually respnd to any e-mails or anything as base as that. You just are not important enough, Although searching thru the Knowledge base is kinda of a art in it self, it's pretty much all you'll get from MS short of spending 35 bucks to get a hold of a tech...
probably what would be most helpfull is learn howto use the
recover console.. you could probably extract a new copy of explorer.exe if the old one is FUBAR...
EDIT.. OH ya if you want to do it professionally.. BE SURE TO BACKUP THE ENTIRE HD BEFORE even touching the PC's! OMG that is the most important thing... doing as something as simple as reinstalling modem drivers can completely F**K everything even if you do everything EXACTLY RIGHT!! First thing to do BACK UP BACK UP BACK UP... If a person wants you to get his sound card fixed so he could play porno mpg's with sound, and he got a virus, and now you try to fix the computer and that virus goes beserk and fries the HD. What do you tell em? uh sorry dude there was a virus.. He goes "it was working when I brought it in, it didn't have a virus, I use the macavi (?) virus scanner that came with my computer 5 years ago(with the 90 day free trial of course), you f****d it up, i love you!". And then when you are told by his lawyer that he kept the finacial records for 30 employees and the contact info for 400 vendors around the country stored in spreadsheets on the desktop in MY DOCUMENTS. Whose gonna get sued? The virus maker? the infected porno site? Microsoft? The sound card maker?.. nope, you!
Just a freindly warning.. don't want to hear about another person losing a business because a customer is to stupid to use floppy disks for backups