have you only got the HDMI plugged into the Graphics card?
have you got something else that has HDMI output you could try the port with (Laptop, TV box, Bluray Drive ect) just to rule out the HDMI on the Monitor as not being the Problem?
have you got something else that has HDMI output you could try the port with (Laptop, TV box, Bluray Drive ect) just to rule out the HDMI on the Monitor as not being the Problem?