Boot Problem - Keyboard Backlight is On - Nothing Else

Early 2014 MB Air A1466 - When I connect the charger and power up the keyboard backlight comes on but nothing else happens. I have tried all the resets and cleaned the connections but still the same. I know the Keyboard was working fine the other day as was everything else (Except the webcam issue that I made a previous post on), but now I am getting this when trying to boot. I have changed batteries to known good ones but still the same (Green light to orange & it is charging OK). When I disconnect the battery and plug in the charger I get a green light but nothing more. I have the kit to test voltages for any board problems but where to start?