I just upgraded to Windows 8.1 now I can't even open a file in excel.

Whenever I click on the Computer to explore to a file Excel Crashes.

This is costing me money in lost billable hours. Who at MS going to fix my issues and to whom at MS do I claim my lost revenue!!!

Try to repair your Office installation.

Here you will find the steps to do.

http://office.microsoft.com/en-us/access-help/repair-office-programs-HA010357402.aspx