Run Office Diagnostics (Help menu in Outlook). If that doesn't help,
repair the Office 2007 installation via Control Panel, Add/Remove
Programs.
If that doesn't help, you can try removing Office 2007, rebooting and
reinstalling.
As a side note, if you have Office 2003 and 2007 installed on the same
computer, you cannot change Office 2003 while 2007 is installed. So if
you want to remove or add a 2003 program, you first need to remove 2007,
make your change to 2003 and then reinstall 2007.
Patrick Schmid