Which version are you using?
If you're using IE6, then you could try installing IE7. If you're already running IE7, try uninstalling and then re-installing. If that doesn't work, get your OS CD and repair the OS installation.
This happened to me a while ago and I just re-installed Windows. If you want to, you could try downloading Firefox or Opera (other browsers are available
) and see if one of them work.
Hopefully, someone'll have a quick fix for you.