Click "Microsoft Excel" from the Recommended Programs section and click "OK" to reset the registered default program to Excel for that file type. Repeat for each file type you wish to reset.

To fix the “Excel file format and extension don’t match” error, first check if the file extension matches its format. Try renaming the file with the correct extension (e.g., .xlsx for Excel ...

Microsoft Excel can open these file types but can't save documents in these formats. When you set file-opening limitations, you can choose from three options to regulate document access further: ...

How to recover a saved Excel file with unsaved work. If Excel closes before you've had a chance to save the most recent changes to your file — but the workbook has already been saved at least ...