Make sure you're plugging in the proper power cables to the card. I believe you'd need at least a 6 pin and an 8 pin power connector for that card. Correct me if I'm wrong. It also may not be booting because your PSU is insufficient. What PSU are you using?
You need the 6 pin and an 8 pin. Get a 6 to 8 pin adapter. It should work fine.