My v6 box used to intermittently not connect through the hdmi leaving a black screen (no audio or video), however now does this every time it is turned on. In the past usually turning TV on and off multiple times would reconnect but now this doesn't really work.
I can reset the HDMI on TV which usually works (easiest way is by flicking Ultra HD mode on and off [LG TV]) - this is not an easy fix for young children.
Change of port and variety of cables doesn't change anything - I still need to do same hdmi reset process as above. No other device has this issue, I tried connecting it through an HDMI splitter we use for some other devices but the same thing happens.