The gt120 in the picture is the correct model, thanks for the confirmation. Out of my experience, those cards have not reported as a type that is likely to fail. You can do one last check and boot up with an open side door to see if the fan of that gpu spins up. Other than that the card is probably ok.
The next search for failure is to check your installation process, meaning - are all needed drivers available, in your case,- is this the correct DVD that you use?
In one of the Upper threads from you, you have mentioned MacBook Air. Is it possible that you somehow have a wrong install medium / DVD from a different device?
Maybe you have the wrong installation DVD? Does it say Mac Pro on it?
There are several different installation DVDs out there, (Full retail, device specific ones (grey) and special editions as well as self created ones) to name view.
Make sure to use the correct original install medium.
As Mr. Kees already mentioned this morning, if in doubt, create your own install USB Stick.
Don’t purchase the HMI cable, I would not go this route.