suddenly have very odd connection issues with a 83inch C3.

My Dune HD Pro One 8K Plus is recognised on the LG TV (name comes up on the correct HDMI input) but reports no signal. I've tried the one 8k with a different HDMI cable into a different monitor and both the HDMI cables and the one pro connect fine to another 4k monitor but not the LG. The LG accepts input on the same HDMI input with say a laptop without issues on the same HDMI cables. Have tried all 4 HDMI inputs but the One Pro suddenly isn't recognized. Rolled back the dune pro firmware - no difference so installed latest again. Reset dune to defaults - no change. Checked video output was auto - no change - then forced 1080p 60hz - no change. The LG hasn't updated AFAIK, deep colour enabled etc.

I don't understand why suddenly it won't work when every other combination I can do is fine? Unfortunately my baby daughter played with the remote when I wasn't there - only thing i've noticed is that when the unit was on standby there used to be a clock visible and now doesn't show now and I can't find a setting to turn it back on, but not sure if it's relevant. Any ideas anyone - I can't figure it out.

Using the Dune 8K player, very happy so far but have a question regarding audio output despite searching the online guide. I like to use wired headphones for late night viewing, but when plugging them into the audio out port I get no sound and the tv speakers continue to play via the HDMI connection. How do I turn on the audio out and mute the HDMI? Thanks