Mine is connected to an Apple TV, but all of them are plugged into a Sonoff wifi switch so when that’s triggered via iPhone or Alexa they all power up simultaneously - would that help you?
I’ve had this for a year, pretty good and the sub makes all the difference.
Could try different hdmi cables, reset tv if possible reset soundbar or your tv is not supported if does then mabey return it order new 1.
Have this one myself and sounds fantastic (and also bought from there) but cannot get the ARC to work on it no matter how hard we try. We currently just use it connected via Bluetooth to our LG tv. It’s a pain though that you have to manually switch it on every time.
I would go for this Samsung one instead it was posted on UKHD yesterday i picked one up for my parents its really good has Bluetooth and a HDMI port as well as an optical port!! Works out around £142 after the discount in store https://www.hotukdeals.com/deals/samsung-hw-k450-21-wireless-sound-bar-14310-with-code-at-currys-3139308