Microsoft Office seems to occasionally damage its settings which results in weird behavour such as: not being able to connect to a printer, commands disappearing from menus, etc.
The easiest way to fix this is to just delete the preferences and let Office re-build a default set. If you have modified your settings much this can be a nuisance because you will have to re-do them all but there is often no reasonable alternative. Its a good idea to backup your Office preferences so they can be restored in this situation.
To delete your Office preferences do the following (this assumes you are using Mac OS X and Office X, for Mac OS 9 just look in the System folder instead)...
1
Quit from all Office programs: Excel, Powerpoint and Word (and probably MSN and Entourage as well, to be safe).
2
Locate the folder called "Microsoft" in your user library preferences folder. In other words: go to your home folder, then the Library folder, then the Preferences folder, then look for Microsoft. Rename this folder to "Microsoft (Disabled)".
3
Start an Office program again and let it re-build the settings. The problem should be solved now.
If you still have the problem you can revert to the old settings by reversing the process above. You can also try moving specific settings files around inside the folders if you think a specific preference file is to blame