Hi Roberto, I have some suggestions for you.
Please remove the power, SSD, and RAM. Connect the power and see if you get three blinks from the power LED when you turn the system on. This will determine if the system is checking for memory.
Check if the memory you are using is compatible and if it is, test a single stick first.
Are you using a good straight quality cable (HDMI to HDMI)?
I changed the title of the thread to something more relevant.