Power up the RPi without the SD card, then you should see a diagnostic screen.
Look for the "display" line, you should see "display: DISP0: HDMI HPD=1 EDID=ok".
Likely you have HPD=0 or no EDID which is not good - appending video=... to cmdline.txt will give you video output but no audio if the EDID is missing.
Check the display cable, if you use some adapter try with a straight micro-HDMI to HDMI cable, if you use an argon one case try without it.
so long,
Hias