samsung 950 pro

for my X58 project, hoping for a 512GB but will consider a 256 if the price is right thanks in advance

The computer is up a running with windows 7 installed on one of the hard drives, but it still won't recognize the samsung 950 pro plugged into the motherboard. I doubt checked and its seated into the slot correctly, but it won't pick it up. Any ideas on what to do? Intel Core i7-4790K Asus...