(Like many of my technology postings, this is really here for my own notes on problems I run into, the solutions I try and what works when. They are updated as I learn.)
After the last windows upate, two of the computers were refusing to open Excel sheets corrrectly. They would open up a Excel Frame but where they spreadsheet should be was completely blank. If you went into FILE==>OPEN==>Previous, it would open files just fine.
The update had enabled Microsoft Office 365 and/or Microsoft Office Student 2016 and chosen one or the other to be the default program to open up Excel files, instead of using Office 2013, the Office Suite we have licenses for.
I used Revo Uninstaller to remove Office 365 and Office 2016.
First I went into "This PC ==> C://". I clicked the View tab and enabled "Hidden Items".
I went into the list of Programs and found Excel 2013, right clicked and open file location. It was OS (C:) ==> ProgramData ==> Microsoft ==> Windows ==> Start Menu ==> Programs ==>Microsoft Office 2013 ==> Excel 2013.
I right clicked on an excel file and selected "Open With…". and inserted the above path.
Windows had to reconfigure Microsoft Office 2013 before it was able to open things correctly.
I then went into settings and Default Apps and made sure Excel had all of its defaults.