The right hand icon is for switching to external HDMI display
The top & left icons I'm not 100% on but is probably to change colour range / switch between night/day mode.
The lower icon is info, and the middle one should be more menu options.
Check that you're pressing the correct button for power, as the All-in-One unit's have a power button on one side and an input select on the other side. Perhaps you're pressing the input select button instead of the power button.