Hello Barbara,
Thank you for posting your query on Microsoft Community.
Please provide more information before we proceed.
Does this issue occurs randomly or while performing some specific task?
Start Excel application in safe mode and check if Excel works as expected.
- Press the ‘Windows + R’ key on the keyboard.
- In the ‘Run’ window type Excel /safe and press ‘enter’.
Note: there is a space between the word Excel and the /
If Excel works as expected in application safe, then disable the add-in(s) by following the steps below and verify the status.
https://support.office.com/en-us/article/Work-with-Office-safe-modes-dedf944a-5f4b-4afb-a453-528af4f7ac72
If issue persist, try repairing Office suite using the following link and check if Office Excel work as expected.
https://support.office.com/en-US/Article/Repair-an-Office-application-7821d4b6-7c1d-4205-aa0e-a6b40c5bb88b
I hope the above information helps. Let us know if you need further assistance.
Thank you.