Were you able to do a systems diagnostics to check for a hardware issue? Please run Dell SupportAssist paying particular attention to the video tests. Make a note of any error messages encountered and post back. If there are none, then this may be a software or driver issue.  
I purchased a Dell 24" VA LED FHD Curved Gaming Monitor (HDMI 2.0, Display Port 1.2) for a Dell G5 SE 5505 FHD Gaming Laptop. When I connect the monitor to the laptop using a (brand new) HDMI cable, I receive an error stating that there is no HDMI signal coming from my Laptop. When I connect the monitor to my OTHER Dell Laptop, it connects and displays instantly. How do I fix the issue with the G5 SE 5505 HDMI out port? It's as if it does not exist.
G5 SE 5505, HDMI out port not working