I bet the HDMI connection is blinking. It's either it's barely on the edge of the supported resolution or refresh or our old friend HDMI Handshake (google that.) There are so many priors that I will not list them all.
Try unplugging the HDMI cable, then remove power from this unknown monitor for 10 minutes. Now apply power and the HDMI cable and try again.
I'm connecting 2 monitors to a laptop 1 monitor connected with VGA cable the other is connected with HDMI cable. I'm able to see my desktop on both monitors but 1 monitor periodically shuts off and back on. How can this be fixed? Thanks for the help.