Doris:
Don't know whether you've tried this yet. Download the
Outlook Personal Folders Backup file from Microsoft. Install it, open Outlook, File > Backup, and save all Outlook data to a safe place. Then go to Add/Remove Programs, select Office 2007 and elect to do a Modify/Repair. Select Outlook only for removal. Once this is done, reboot and reinstall Outlook. Go to File > Import and Export, to import your Outlook data back again.
Hope this helps.