HP Z800 RAM Upgrade

Hi, 

im upgrading my RAM on a HP Z800 and ive got a problem. 
I have got the original RAM that came with it (2x 8gb ddr3-1333 RDIMM) and ive got the aftermarket RAM i just bought (Same specs but from Samsung not Kingston).

The PC boots up with the original ram, but not with the new ram. It doesnt boot with both either. 
I already tried all possible RAM-Socket-Configurations and it still doesnt work. 

Help :/