Could be a lot of things.  Here is what I would try:

1) Try running the Internet Explorer in Safe Mode with Networking.  If it runs ok here, it is most likely an add-on that is causing problems.

2) Try exploring the internet with Windows Explorer.  If this works, it would also suggest a bad add-on.

3) Run HijackThis and look for anything suspicious. 

4) Look at your Event Viewer for any abnormal entries.