iMac / Programs freeze at random times.

Hello there,Macrookie03.

The following Knowledge Base article has some practical steps for troubleshooting issues with applications not functioning as expected:

Mac OS X: How to troubleshoot a software issue

http://support.apple.com/kb/ht1199

In your case, since it seems to be isolated to Excel:

If the issue occurs in one application only

For example, one application does not open or unexpectedly quits. Mac OS X v10.4 and later can help with applications that unexpectedly quit by offering to open the application with default settings. If this doesn't help, skip to "Drag the application to the Trash and reinstall it if the issue persists..." below.

1. Make sure you are using the latest version of the software. Check with the manufacturer if the product is published by a third party.
2. If the issue only occurs while using a specific document, try creating a new document or replacing your document with a backup. Your document may be damaged. If possible, try testing with either a new file or a known-good file.
3. Drag the application to the Trash and reinstall it if the issue persists. Some Apple applications that may have been included with your computer can be reinstalled by using the Install, Restore, or iLife disc that came with the computer. See these links for more information:
   • Mac OS X v10.6 Help: Reinstalling applications that came with your computer
   • Mac OS X v10.5.5 and later: Installing optional and bundled software
   • Custom installs in Mac OS X v10.

Thanks for reaching out to Apple Support Communities.

Cheers,

Pedro.