Logos (Mac) has died. I need to resurrect it, but it's just a zombie.

Logos loads, but never shows a screen. I can't even tell you what version I'm running, because of this. 

I've force-quit, I've rebooted, all to no avail. Suggestions? 

I'm on a 2010 imac with 100Gb free on my SSD, 16Gb RAM, latest build of Sierra.