There's plenty of similar questions on the internet about this board, just google "GA-970A-DS3P mining" and you'll find identical topics from people not being able to run more than 3 cards. Check whether you have the latest BIOS, and if not, update to the latest version. Also check the revision of the board you have, there seems to be multiple revisions of this model. Reinstalling windows helped some people, not sure why though but might be worth a shot.