1st thing to check your screens looking at the right input source feed if it has multiple ports My dell has 2 HDMI, a DP and a VGA!
Also you can is plug the screen into something like a laptop or other PC make sure it gets a video feed, if not try a diff cable see if that's at fault.
If you get a video signal from a diff device then its the video port your using not outputting. Try using a diff cable/port combination of the GTX card, Does your MOBO have onboard vga? That may not auto disable so you could see if you get an output from that?
Last option remove and re-seat the GTX card and re-boot pc. You could test the card in a diff PC or vice versa test a another card on your mobo to see if its the card or mobo at fault.
There are no quick fix's just a process of testing