I am (almost) sure my problem is not specifically related to Excel , but I'll try...
Since last couple of days, on double-click of the file in File (windows) Explorer a new instance of Excel is launched and I get a message
"File ... fullpath... or one of his components not found. Make sure.. blah blah"
When I try once more, another instance launches, same message.
Open File from Excel menu works normally.
It's probably something with the registry.
Any hints? Should I reinstall?