Have you tried what JP suggested in #9 below? Have you checked to see that Content>My Profile actually has entries and hasn't been accidently cleared?
You can also check your registry settings but backup before you make any changes. These are the directions for adding additional domains but suffice to enable you to see if you have them listed where they should be.
"To add search domains, run the Registry Editor and navigate to HKEY_LOCAL_ MACHINE\SOFTWARE\MICROSOFT \INTERNETEXPLORER\MAIN\URL TEMPLATE. You’ll notice String values named 1, or 2, or 3, etc., with values set to “www.%s.com,” as the format. Right-click the URL TEMPLATE key, select New, then String Value. Name the String value the next logical number. For example, if 1, 2, and 3 are already entered, name the new one 4. Double-click the new String value, and enter Value Data using the same format (www.%s.xxx, where xxx is the domain you want). So, if 3 is the last number displayed, create a new String Value named 4 by typing 4 as the String value. Then, to add the .NET domain, type www.%s.net for the Value Data."
Additionally, check out the registry settings mentioned at this site: