My gpu won't display anything

[nicbread]

Hi, I put my 7870 into my old i5 760 PC to make it a gaming machine, I know the 7870 works and I know that the i5 760 machine works. The machine powers on but won't display anything. I have an AWARD based BIOS and I get the beep error 1 long beep and followed by 2 short beeps. I have taken the CMOS battery out then put it in, but that didn't fix it. I tried my GTX 550ti and it worked just fine. Any help?
Thanks in advance

 

[chemmajorp53]

Did you update the bios on your motherboard? Might be worth a try