Hi Cthonix ! Sorry for the delay.
What's the brand and model of the computer ? If it's a custom build then what are your complete system specs, including brand model and wattage of the power supply (check the link in my sig).
What product key do you own and what XP CD did you use to reinstall ? What service pack is included on the CD ? Check that the XP CD isn't scratched, try to copy its content to some folder on the computer.
If the XP CD is ok, it may not have the proper drivers for your system (if it's some brand computer you'll need the OEM CD that includes specific drivers for your hardware) or you may want to try with an XP SP2 or SP3 CD.
Could also be some hardware problem, Ubuntu requires less ressources than XP and may start where XP doesn't.
What's the brand and model of the new hard drive ? Make sure it's set as master and hooked on the SATA1 port or on the primary IDE controller.
Open the computer case and check that there's no dust on the fans and heatsinks. Check that all the fans are spinning (CPU, video card, power supply, case fans).
Enter the BIOS at startup and look for some hardware monitor or pc health status screen. Report your temps, fan speeds and voltages from there.
Test your ram : download, unzip and burn
memtest86+'s bootable .iso image file using a burning software that can handle .iso files. Enter the BIOS at startup and set the boot priority to CD-rom first. Leave memtest run overnight or at least do 3 full passes (3 times the 8 passes) on your memory. It's advised that you test one memory stick at a time, removing the others from their slot. Report if it finds any error and double-check memtest's results with
windiag as it runs different tests.
If it's a custom built computer then unplug unneeded drives, pci cards and USB devices, use the onboard video if available, leave only one RAM stick in the DIMM1 port and retry to install XP with only the system drive and CD drive. You can reinstall all other devices once Windows is installed.