Hello box is set to active start. Welcome screen when reboot. Nothing when turning on from standby just screen resolution numbers show and active HDMI port number.
I assume that is the HDMI port that the 360 is connected to.
You said in your first post that you reboot the box after 15mins, so it's been a blank screen for all that time, is the reboot you do just switching the box off and on with the switch on the back of the 360 ?
What happens if you just turn the box off with the remote and back on again is it just the same. Do you get any error messages at all and are all your recordings OK.
You could try a factory reset if you haven't already tried that, go to Settings > System > Factory Reset
It's only a partial system reset and not a complete factory reset. You are given 2 options,
Choose Keep Recordings, that means you won't lose your recordings and any planned recordings or series links you've set up, you will have to sign into your apps such as iPlayer, Prime, Netflix and ITV Hub again, also Match frame rate and Standby power consumption will go back to their default settings if you have changed them.