I should also add by way of context: HPs have had issues with their motherboards in the past. In a previous life I sold a few hundred to a single firm and had 20% of them returned on warranty. Naturally my client wasn’t too pleased, and neither was I.
On the upside, HP is good with their warranties, and they will look after you properly. Once your machine is working right it will work for a very long time. I’m writing to you on an HP that has been abused in every way possible. It is missing keys I’ve hammered the keyboard so bad, and there is a wear-spot beside the touch-pad, where all the silver paint is worn off. The texture is worn off every key remaining, and the keys are polished to a shine. If it were a horse I would have to shoot it. And I’d get done by the RSPCA for horse abuse. They are good machines, generally.
Take your time since you still believe that you have your files out there. You might try chkdsk from a floppy os. If worse comes to worse, you can always rebuild your op system assuming you have a complete win xp. It gives you the option of saving files it finds from the previous op system when you go into a repair mode or even rebuild. If you have another computer running in your home, use it to troubleshoot your problems as well. I have an AMD FX64 running Vista Ultimate 32 as well as a pentium running Windows XP Professional which I use occasionally to get myself out of difficult situations. Good luck.