If you are not getting ANY video from the HDMI, DO make sure it has not come unplugged from the back of the unit.
Have you gone into the video set up menu?
Make sure you only set the video resolution to the highest your TV can support.
I made a mistake and set for 1080P and had a hell of a time getting a viewable picture back (had to reset and connect a AV cable to see the menu to fix it - there is no "undo"). Then I discovered "Factory Reset" see photo
The default resolution is 480i - My TV only goes up to 1080i !!
Also set the TV type to widescreen if you have one 16:9
Video should be P-scan or Interlace YUV (Don't remember which one I use)
If you lose video or it goes squirrely:
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW