Ok, after the computer reboots, after it gets passed the BIOS screen, start pressing F8 until you get to a screen with multiple options about Safe Mode, etc. CHoose the one that says "Disable restart on system failure," then choose XP Pro on the next screen. Let us know if you get a blue screen error.
If you do get a blue screen with white text (BSOD), then write down the following information before you restart, and post it here:
The words in all caps at the top (something like IRQ_IS_LESS_OR_EQUAL) or something like that; and also the STOP error code at the bottom of the screen. It'll be in the following format: 0x000000##, where ## = a combination of numbers/letters.