radeon Vidcards DOA 3 in a row.psu problem?

[ProdigalGeniuz]

i'm having a dilemma whether it is my psu or im just super unlucky.my psu is antec hcg 900watts.it works with my current radeon 6870, sapphire toxic r9 280x and radeon 7990. but it does not work with sapphire 290x, xfx 290 and sapphire vaprx 7970(all no video signal output) they all require a 2 x 8 pin. i have 2 x (6+2) pins.

 

[smeezekitty]

Have you upgraded your motherboard BIOS yet?

 

[ProdigalGeniuz]

yes i did..i have sabertooth z77 upgraded to 2104 bios i think..do you think it's a mobo incompatiblity..i tried on both slots.never worked.

by the way it does gives out a beep..and i can hear windows load fine.im pretty sure there is no video signal