MS Office has a repair capability you can find in the Programs and Features applet of the Control Panel. Look for the MS Office entry & click on it, then click on Change. That will start an Office task with a REPAIR radio button. Click on that and click on Continue. Since you didn't say which version of Office you have, I'm using the Office 2007 version for reference. If you have a different version, details may vary.
If the above doesn't work, you can always uninstall and reinstall Excel.
Edited by wpgwpg, 16 June 2014 - 02:29 PM.