Here's a head scratcher .... can't figure this one out. Mac Pro 5,1, Mojave 14.4, Sapphire RX580 video card. Video displays fine when using AOC monitors with DVI input. I use DVI to HDMI adapters to plug both monitors into the video card HDMI inputs. Looks great. However when trying to use a single new Dell monitor with only an HDMI input and connecting to the RX580 using just a standard HDMI cable no video is detected. Doesn't make sense. Any thoughts appreciated!