Graphics card advice

Why would you buy a worse card, take it to the warranty get a replacement, if its really faulty.
I don't know how you determined the graphic card was faulty as errors can come from various reasons (memory, psu, drivers, software.....)

If its faulty and under warranty then return it

But how do you know its a hardware problem?

There was no power to mouse or keyboard and no display when 7850 was in. i tried 1 stick of RAM, resetting CMOS, rewiring system but still the problem persisted. I then took the graphics card out and tried it. Everything worked fine except i didn't have the right VGA cable for onboard graphics. I then got another graphics card from an old pc and am now using that instead and everything is fine. I might try putting the 7850 in again though.