In your BIOS, is your PCI-e set to GEN3, or AUTO?
I had a similar issue myself with testing a card for someone who had a different problem. That problem turned out to be a bad driver, but part of the testing was throwing in an old card that I knew worked! This is where I ran into a similar issue to yours... I couldn't get display either when I put the old card in, and found out that the PCI-e slot was set to GEN3. I put it back to AUTO, and..... BINGO!
It might just be a bad cable, but check that too.