Instructions
Click on "Start" and choose "Control Panel" from the Windows Start menu.
Select the "Uninstall a program" link.
Locate the "Microsoft Flight Simulator X" entry in the list of installed applications and click on it.
Click on the "Uninstall/Modify" icon in the window's toolbar.
Select "Next" and click on "Repair." Click on "Next" again. The installer will now repair your "Flight Simulator X" files.