Sounds very much like a jQuery conflict which is causing the AJAX to fail. Very rare on the Admin side of things but not completely unheard of, I would have hoped the error trapping would have picked that up but it might just be happening too early and not even trying to run the install AJAX scripts because jQuery has already errored out and stopped.

If you know how to use the web console to look for script errors then that is what I would do. If you do and you can send any messages we may be able to ascertain what the conflict is...