PC wont POST after installing new GPU

[0412041]

Im buliding a new pc recently and my spec are:

i5-3470
CM GX550w
Asrock H77m
Sapphire HD7850 OC 2gb

Now the problem is, after installing the hd7850, the pc wont post or boot, not even bios, it just black screen, and i can boot in windows fine with intel hd graphic or another hd7850 (non-oc) from my friend.

550w should be more than enough for a hd7850 oc and what i have tried are:

setting the bios
reset cmos
update cmos
check the power connector

is it clear for me to declare it is a bad or faulty gpu?

 

[J_E_D_70]

I'd say doa given a similar model works fine. Doh!