I have both Office 365 and Office 2007 installed on my computer and have had for at least 5 years. No changes to the computer recently other than the usual Microsoft updates.
I have the Office 365 version of Excel selected as the default program for xlsx files, but when I attempt to open any Excel file, Excel 2007 opens but does not open the file. I can open either Excel 2007 or Excel 365 and then open any file without a problem. But I cannot just double-click on an Excel document and get it to open. This is a new issue that I've only seen today.