I have a Mac Pro 1,1 that I am attempting to upgrade for the purposes of updating it to El Capitan. I hadn't used the computer in a year or two, and there was not an HDD installed in the system. (I pulled drive from it a while back for another project) When I stopped using it a few years ago, everything worked normally. I installed a new HDD, and attempted to boot from a USB Installer, but did not get video from GPU (7300GT). I am using a DVI to HDMI cable to plug into a TV ( I have also used same cable to plug into a computer monitor, no joy). I have reset SMC, PRAM, and reseated GPU. Computer boots up and chimes, just no video. Drive doesn't have OS X on it, so I cannot remote in from another mac to see if GPU is in system profiler. I have a Mac Pro 5,1 at work with an Nvidia GPU in it. I brought home the Stock AMD 5770 from the 5,1 and installed it in the 1,1. Still no video. Attempted with DVI to HDMI, and mini-display to HDMI cables. I took the HDD to work, installed it in the 5,1, and reinstalled the AMD 5770 in order to boot from the USB Installer and install OS X 10.7. Idea was to set up account & enable remote log in so that I could install into 1,1 and remote in from another mac. When I installed 5770 into 5,1 I did not get any video. Card fan spins up, and computer chimes, but no video. I didn't have my laptop with me, so I wasn't able to remote in at that time. My Nvidia card is not flashed, so I cannot boot into recovery without the 5770. Is it possible the 1,1 is "killing" cards somehow? The only other thing I can think is that because there are no drivers installed GPU isn't displaying video, but that doesn't explain why the 5770 no longer works in my 5,1. Does anyone have any suggestions?