reinstall windows

I installed windows xp pro on my other computer, and it wont accept my serial #. So now it wont work because i have to activate it. When i phone support they said i can only use it on one computer, so now i have to reinstall windows with home edition, and use the serial # on side of that computer the only problem is, i can't seem to get to the install window, i put the home edition cd in and it just keeps rebooting to the windows log in screen, i even changed the boot sequence, do i have to format with the pro edition? I am very confused, please help. thanks

 

never mind i figured it out, it was trying to boot from the other cd drive so i disabled it, now it is working,