Harddrive Problem

[Noodlez]

Background to the problem:
My computer was working fine, I was building a new computer and didn't have a new harddrive so I decided to take my harddrive and just throw it in there. New computer works fine with my hd and I run into no problems. When I connect my HD back to my old computer, first I accidently connect it as a slave to my CD drive and I was quickly made aware of that, when I change it back to normal it goes into an infinite restart loop. So I try safemode and it stops loading at Mup.sys. I googled the problem and TONS of people seem to be having this problem but there is no definitive solution to it. Right now I'm on the new computer with the harddrive from my original computer. This makes no sense to me why it would even work in one computer and not another. Any one have any ideas? I already reinstalled windows did chkdisk fdisk and all that garbage. I want to avoid formatting just to save a headache.

[quasi-modo]

Well hold on, you are trying to move the hard drive from one computer to the next? What vers of windows are you using? What are the chipsets and processors?