I am not sure so I will only take a stab at this.

How old is this PC? Some older equipment has issues with XP because of the antiquity of some drivers needed.

Another point could be that you have no drivers needed to continue. What if your mainboard is causing troubles because your PCI bridges are not communicating?

Yeah, sounds wrong, but I have seen it once.

I would:

1) do a total reformat, making sure that it completes by making it receptive to a windows op sys. If it allows, format it to DOS if need be.
2) make sure that you preload any drivers you may need to insure that your mainboard is ready. Contrary to some, this is necessary at times with certain makes and models.
3) make certain that your XP disk is undamaged and not corrupt.
4) install a total upgrade/new install.

Lastly, XP has an autoboot version, you might need to press your auto boot key. This could be F5, F8, DEL, or any other combination of said keys. You may need to visit your boards designer site to ascertain which key this is. WHEN exactly you need to press this key should be evident because your bios will tell you to "Press it now" (paraphrasing)

Good luck.

any or none of this advice may be ineffective.

Ahh, I missed the hardware but was right methinks.

Glad you got it sorted.