There's a lot I don't know. Not sure why it is freezing up on bootup; likely some key file is missing. You may have even picked up a virus. But I'll suggest this...on the initial BIOS bootup when it checks your computer, you should hear a single beep. If so, the hardware is functioning. Which would seem to indicate you have a software/OS issue. I would then suggest a safemode bootup. While in the BIOS startup routine, after you hear the beep, press and hold F8. You should then be given the option to start in safemode. This loads Windows with minimum drivers, etc. Once computer has finished booting, then I suggest running checkdisk to ensure your harddrive is serviceable. If so, then try running system restore to restore windows to a previous version as you may have picked up a virus. You can also run your viruscanner in safemode.
If the computer wont boot into safemode at all, then you've gone into a new realm. If your checkdisk in XP fixed errors, I'd wonder how you got those errors to begin with. It could be the harddrive has indeed gone bad, or a virus has had its way with you. I would try a complete re-format then. If it can be re-formatted, then it was probably a virus that got you.
If nothing else, with the harddrive in the winXP computer, you can at least save any files you may want to keep and either do a complete format and re-install or if it is the harddrive malfunctioning, get a new harddrive. Good luck. This is one of those frustrating times for a computer owner.
There is also this that might help... http://windows.microsoft.com/en-us/windows/repair-recovery-help#repair-recovery-help=windows-7