Roll back the latest Excel patch, people: it's a crasher.
Of course, not every Microsoft user will be able to roll it back, in which case you'll have to sit tight, and hope nothing goes wrong before the next cumulative update.
However, this Knowledge Base article advises that Excel update KB3118373 has led customers to report that “Microsoft Excel has stopped working”.
Redmond doesn't know why, but it's stopped further release of the update and published removal instructions for Windows 7 through Windows 10. ®