Recently upgraded to Win10 from Win7 and that action removed my MSOffice 2007 but saved some of my documents. I re-installed my MSOffice 2007, but now cannot open my Excel spreadsheets. When trying to do so, a pop-up appears asking which app I want to use in order to open the spreadsheet ... and Excel is not an option.

Another twist: When I now open a blank spreadsheet in Excel, and click the 'open' tab (upper left) I can locate and open the spreadsheet I want - and work on it, but cannot save it properly. It never saves to "excel" but defaults to some app that won't re-open the spreadsheet properly.

Your help, please.