Try resetting Internet Explorer:
1. Click the Tools menu, and then click Internet Options.
2. On the Advanced tab, click Reset.
3. In the Reset Internet Explorer Settings dialog box, click Reset.
4. When Internet Explorer 7 finishes restoring the default settings, click Close, and then click OK two times.
5. Close Internet Explorer 7. The changes take effect the next time that you open Internet Explorer 7.
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Resetting Internet Explorer will reset the browser to default settings. Although the Reset Internet Explorer dialog claims that bookmarks/favorites should not be affected, everytime I tested, all favorited sites were deleted, so save all your favorite sites if they are important to you.