This subject has reared it's head on more than one occasion but solution this may help:
Issue: Fusion starts but hangs almost immediately with a black empty rectangular box on the screen.
Solution: Fusion likes to Network Render. I have a Synolgy 1515+ which was set to auto sync some of my working folders with the NAS unit. This presents itself as a live network link and effectively locks Fusion out. I stopped this process and the black triangle issue simply went away.
All I have to do now is figure out a way of mapping my folders to the NAS unit again. Quite simple really
Hope that helps someone out there.
LJ