Can't go fullscreen

Okay so when i boot up my game, it opens in a little window. 

Then i alt-enter to go to fullscreen, the screen turns black for a sec (as if its actually switching to fullscreen) but then it goes back to the window.

When i select fullscreen in video settings, it's also like that. Borderless works but brings my GPU usage down to 60% and my fps to about 30.

Running on a GTX 960M (i know), i7 4720HQ, HDD and 8 gigs of RAM.