This looks similar to the '870' series... first unplug from the mains for a while and then reconnect. Assuming the machine power up OK and comes out of standby you should next press and hold the stop key on the front panel. Whilst still holding the key firmly down, now press the standby button on the front panel. The machine should switch off and reset. Wait a few seconds and then try taking it out of standby again.
If it has reset correctly it should now be in the 'out of the box' state and allow you to set it up correctly.
If by chance it still won't play ball then I would disconnect any external HDMi and Scart leads and repeat the process again.
And just to cover all bases, make sure that your remote isn't transmitting all the while. Take the batteries out to be certain.
The reset will not delete any HDD recordings. Also be sure not to have any DVD in the tray whilst doing all this.
Good luck 🙂 these are fantastic machines and I have two (HXD 870's) one of which gets around 5 hours or more a day use. We time shift everything.
