Can't load MuseScore

I updated to the latest version and it worked fine two or three times.

Now when I try to load it, a black question mark appears over the app icon. I thought maybe I'd just load one of the songs and it would work around the problem, but all my scores are now associated with Skype?!

Yes, I tried shutting the computer down and restarting. Still having this issue.

Thanks for your help.
Matthias Hoefler