How are you checking for a black screen? Alt-tabbing out of a full screen game will cause it to stop rendering, which can mean a black screen in OBS.
This happens with all games?
Have you tried running OBS as admin?
Are you using any programs that overlay information in the game? If so, close them completely. Examples are MSI Afterburner, EVGA Precision, Razer GameBooster, TeamSpeak and/or Mumble overlays, etc.