Excel for Mac - Oct 2018 update issue

[AJE-1]

I updated my Excel for Mac in Oct 2019 (regular and now it won't open any past files. Can anyone help? The software will open and it will generate new spreadsheets, it just won't open any that I have made in the past. 

[#2]

Have you considered opening them in numbers, save in Excel format then try to open in Excel