Premiere Elements 15 won't start - yesterday it did, today it doesn't, tomorrow who knows?

It's as simple - and incredibly frustrating - as the title suggests.

Yesterday, I was editing a project, rendered the video, put the computer to sleep. Premiere Elements 15 had been fine throughout.

Today, I come back to finish the project: PE15 simply WILL NOT start.

I click the icon, the splash screen opens, then I can choose the name of my project, or open, or start new project and NOTHING happens.

The blue wavy "stuff is happening, honest" bar washes back and forth under the splash screen after I make my selection, but ultimately leads to nothing.

I can launch Organizer and see the video assets. Clicking edit in PE from here - same result as above.

I can try to launch PE15 from my Applications window, from the Dock, from Launchpad, from Recent Items - anywhere on my Mac. Same result: nothing.

NOTHING has changed on my Mac since yesterday afternoon!

What gives?

I installed PE15 and Photoshop Elements 15 a couple of weeks ago. I bought them new as a twin-pack install DVD.

Photoshop is working fine. Organizer is working fine. Premiere is not.

MacBook Pro Retina 13" (2015), 2.7GHz, 8Gb RAM, 256Gb drive. Mac OS X 10.12 (Sierra).  

Any help, ideas, suggestions would be appreciated.

Thank you.