I have the same issue here, my notebook has a intel hd graphics card and a nvidia GTX880M wich is performing perfect with everything except with jriver, I wanted to try to run jriver with my gtx880m ( right click the mc20.exe file and choose run with the nvidia card) but i have the same issue then black display. i have it on the built in laptop screen as well as on ther tv connected to the hdmi so my thoughts that it might have to do with the hdmi port being connected to the intel card isnt it. The problem is that the intel card struggles way more with the higher settings in jriver (red october HQ, hardware accelerate, video clock, bitstreaming) I was away from j river for a while but upgraded from mc18 to mc20 now, but this problem with the nvidia card is just weird. i had a look on internet as well for similar issues but couldnt find it.
I am running the latste driver bu the problem was there in an older driver as well so i guess its something in j river instead of driver issue or even as ppl suggest here a faulty gfx card.
hope there will be a solution for this
*edit* i forgot to mention that i'm running windows 8.1 x64 and my notebook has a core i7-4700HQ cpu, 16gb ram, and a 500gb ssd.
also whenever i do try the nvidia card to run jriver i cannot close the program and can only close it with taskmanager