Well, I'm new to this board, and I work for a computer repair shop, so here goes...
I have had 3 seperate computers in the last couple days that have all had the same issues. They will all boot up to the "Loading Windows XP" screen, but will restart immediately after. If I run safe mode, they will stop around loading the mup driver, then will restart. Another tech I know of has said there is a virus/trojan circulating that has caused registry changes that will ultimately cause the hard drive to fail. Any inclinations or thoughts on this?
I would not bring my computer to your repair shop. A virus/trojan cannot cause a HD failure. Did you try booting from a Windows XP CD, starting a Recovery Console and running chkdsk c: /p/r until there were no errors? You could also try a Repair installation of Windows. Why does everyone think viruses/trojans cause every computer problem?
Virus can absolutely cause a software program to fail - The operating system is a software program. If the virus keeps chipping away at parts of the main core eventually it will cause a total failure. Also, if it inserts its own hooks it can prevent a repair or a reinstall without a full reformat.
I have had several of these in the last few weeks and it is unrecoverable at this point. You can get your files by slaving the drive (sometimes) but the operating system is gone.
There was someone on this forum that tried to claim a virus could make the heads of the hard drive crash into the platters. Since the heads or the platters were not designed to move vertically, such a thing would be impossible. The only things that can cause a head crash are severe physical shock or debris between the platters and the heads.
No, viruses cannot cause hard drives to fail. They can destroy data... but physically the hard drive will be just fine. Now, if there was a virus that could infect or wipe out the firmware of a hard drive (like the Chernobyl virus did with BIOS chips)... then it certainly would be possible to render the drive useless... but firmware can also be rewritten.