As with any similar problem, first things I would ask is..

1. What, if any, changes were done.. software installs/uninstalls.. ?
2. That indeed, it only affects that one browser.. ? (not a larger issue)
3. Have you tried an IE repair ? and a system file check ?

maybe some info/links this page here, might help.

In the end, if you need a full install of IE, then you could visit this post.

edit : I'm such a slow researcher/typist.. still I hope my post wasn't for naught..