Follow the instructions on this page to repair your Office 2010, Office 2007 or Office 2003 installations to fix errors in Outlook.
For help repairing Office 2013 or Office 2016, see How to Repair Your Office or Outlook Installation
Because Office Diagnostics was mostly useless, it was removed from Office 2010. You'll need to use the repair process in Control Panel's Add or Remove Programs to repair Outlook.
To start the repair process, open Window's Control Panel and locate Add or Remove Programs under Programs and Features. If you are using Windows 7 Category view of the Control Panel, choose the Uninstall a Program link under Programs category. In all versions of Windows, you can also type add remove programs in the Search field to find Add or Remove Programs.
Once Add or Remove Programs is open, locate your Office 2010 or Outlook 2010 standalone installation in the list of installed programs and select it. Then click the Change button. In Windows 7, it's at the top of the list. In Windows XP, it will be to the right of the Office entry.
Office diagnostics will repair some problems but is mostly useless for serious problems, however, you can use it as it does no harm and may fix your problem. just don't get your hopes up - it's not an "end all, be all" solution for all problems plaguing Outlook. Doing a repair is generally better although it takes longer and you may need the Office installation source handy.
Repair Office 2007 Installation
To repair your Office or Outlook installation, open the Control Panel and locate Add or Remove Programs. If you are using Windows 7 Category view of the Control Panel, choose the Uninstall a Program link under Programs category. In all versions of Windows, you can also type add remove programs in the Search field to find Add or Remove Programs.
Locate your Microsoft Office install in the list of installed programs. Select it, then choose Change. If you are using Windows 7, the Change button is above the list of installed programs (as seen in the screenshots for Outlook 2010 on the previous page.)
Choose Repair on the next screen and click Continue.
Run Office Diagnostics
Expand the Help menu and choose Office Diagnostics to start the Diagnostics wizard.
The Office Diagnostics wizard opens. Click Continue to begin.
The next screen shows you everything the diagnostic routine checks. Click Run Diagnostics to begin.
While the diagnostics are running, the dialog updates with the results:
To use Detect and Repair, insert your Office 2003 cd then go to Help menu and select Detect and Repair. Next, you'll choose whether to restore missing shortcuts and discard customizations. Click Start and the process will begin.
Run Repair from Control Panel
To repair the installation by reinstalling it, insert your Office 2003 CD then go to Control Panel and click on Add or Remove Programs. Locate the Office or Outlook installation in the list of installed programs and click Change. (If you are using Windows 7 Category view of the Control Panel, choose the Uninstall a Program link under Programs category.)
Next, you'll choose Reinstall or Repair option and click Next to begin the process.
When the process is complete, your installation will be repaired.
This video tutorial shows how to repair an Office 2010 installation. The process is similar for Office 2007 and Office 2003.