Computer Freezes at XP loading screen

I have been trying to solve this problem on my brothers computer for a while now.
It just gets stuck on the XP loading screen. (The screen Freezes)

I have tried changing the hard drive. I put windows 7 CD in and it got stuck on the loading screen for that. Then after a few attempts it would stop booting from cd altogether no matter what i tried. So i tried changing the CD drive just to rule that out. Then i tried changing the Ram.

This has got to be the motherboard right?

I can't try changing the motherboard as i have none spare compatible. I just want a second and third opinion before i go and buy another one.

Thanks.

You can help narrow down the problem by hitting f8 after the bios posts to enter the windows boot options (where you would normally go to boot into safe mode). If you select
Enable Boot Logging it will log the boot process to a text file named Ntbtlog.txt that gets saved to the system root folder. If it gets far enough into the boot process to write out the text file before freezing, you should be able to look at the log and see the last thing initiated before it freezes, which will usually be the culprit.

Also, have you tried reseating the heatsink with some new thermal paste? The white goop used in most computers dries out over time and can cause overheating that often results in freezes in windows.

I have been into the boot options on this computer before and i don't remember seeing "enable boot logging" but i will check again when i finish work.
Heat should not be a problem because i know this computer has a very low temp around 30c on load. I have also seen the temperature in the bios which was about 15c.

Have you tested the power supply in a known working computer to rule it out yet?