Hi, Pieterst!
This is somewhat of a standard reply **, but reinstalling Office 2011 might (vielleicht) address problems that you may be experiencing.
The current version of Office 2011 is 14.4.8.
First - find your Office 2011 install disc with the product key # - and only then remove Office according to MS instructions
http://support.microsoft.com/kb/2398768
Or go here to DianefromOregon's site for help removing Office 2011:
http://www.officeformachelp.com/2012/12/office-for-mac-2011-remove-office/
Then Reinstall from DVD
Then enter your Product #
After successfully reinstalling Office 2011, update your Office product using the Software update within Office called Microsoft Update or going to the Help menu within Word or Excel or PowerPoint and select Update.
It may take a few times before you get to final upgrade to current Office version.
It should be 14.4.8 as of current date.
How to locate product keys
http://support.microsoft.com/kb/2279109
or here on locating product keys
http://office.about.com/od/MicrosoftOfficeMac/a/Best-3-Ways-To-Find-Microsoft-Of fice-For-Mac-Key-Codes.htm
Note is updated as of March 5, 2015
**Wir können etwas anderes versuchen, - wenn das nicht funktioniert.