I just got me the game and loading into the HUB worked all good. So I tried to select me a mission to slay some heretics but when the mission i supposed to start nothing happens, well the Music keeps playing and I have to close the game via task manager. I tried out other Missions to see if it was just a one time thing but nope happend on all missions. So I changed graphic resolutions and stuff, same problem. Made a new character to see if that might help and still nothing.
EDIT:
So on the Steam Disscussions they found a solution to the problem.
Simply start a co-op match :D Yes it might take a while to find enough players, but thats up to the time when you are trying ^^
After that you can play the single player Missions without any problems :)
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I'm also having this problem, the game runs fine in the HUB area and star map until I try to load up a mission. The game freezes on the first frame of the mission while the audio keeps playing and there's a thin black bar that runs horizontally across the bottom of the frame. 
Here's a screenshot
Im having the same issue. . Ive tried Lowering graphics, Turning Comparability mode on, Re-Installing, Loading different Missions , nothing worked , , , What to do ???
Same here with the same result´s
fix it ASAP !
Same problem, plz write if you Find a solution.
Same here. I've verified that I'm running off the correct GPU, and ensured all my drivers are up to date. Nothing I've tried has worked with regards to actually playing the game. I can access everything on the command ship just fine, but missions never fully load and it just freezes.
So on the Steam Discussions they found a solution to the problem.
Simply start a co-op match :D Yes it might take a while to find enough players, but that's up to the time when you are trying ^^
After that you can play the single player Missions without any problems :)
Set this current order state as My default.