Before you try doing an XP reinstall, make sure your hardware is sane.
Download the memtest86 memory diagnostic and burn it to a CD. Boot from it and test your memory.
Next you want to check if your hard drive has bad spots and that's why you system won't boot. No use trying a reinstall if the drive is not in good shape. There are several ways to do this. You could download a drive diagnostic from any of the biggies (Maxtor, Wsetern Digital, etc). You could also download and burn a bootable CD copy of knoppix. You'll be able to read your entire hard drive and see if their are any disk errors.
Knoppix also has the memtest option as well--at the boot prompt, just type in "memtest" without the quotes, and it will run the memtest86+ program.