If you have ABBYY Finereader installed on your system, the Word and Excel add-ons that come with this program may cause Word or Excel to crash at every startup.
Starting in safe mode and then removing the add-ons, a commonly suggested fix, only worked for Word. For Excel I was unable to start the program, even in safe mode.
The best fix seems to be to simply uninstall Finereader. If this fixes things, you can later reinstall the software–just make sure to deselect “Microsoft Office Integration” when you install.