Gpu cause no signal on screen

[lemmoncake]

hi guys! i have built a computer with an asrock extreme 4 mobo and without my gpu in it runs windows fine and the whole build it works fine and my monitor works fine!

but....

when i insert my radion 7950 into the mobo and turn it on i get a blank screen and no signal pops up then the screen goes into power save mode!

i still have the cable for my monitor plugged into the mobo as i dont have the right cable to plug it into the gpu(need a hdmi lead)...

i was wondering if it was just that because i have it plugged into the mobo and a new cable that plugs into the gpu will solve it or if the gpu is faulty?

i dont want to waste money buying a new cable that isnt going to work.

PLEASE HELP
im a bit of a computer newbie!

 

[lemmoncake]

the gpu needs eather a div to dvi or a dvi to hdmi

so if i do need another one what is best?