Msn Messenger 7.5

I recently was given a new Dell desktop. It works very fine except when I tried to install 7.5 the whole machine locked up. When I finally managed to uninstall the program ( it was not easy ) I looked for conflicts, and the only one I could see was windows messenger. Turned that off, tried again, same thing. Ran a registry check and it found 163 errors all to do with 7.5. Any ideas what would be causing this? I use MSN for work quite a lot and no other forum has been able to suggest a viable fix. Thanks in advance, Iain