Tablet processor is working, but screen shows nothing

My A1-840 screen suddenly stop working. When I push power on button, the screen brigths slighgly from the border but nothing appear on it. I connected the hdmi cable to a LED TV and verified that software is working OK and the touch control is also working. How could I determine whats wrong?. Is the digitizer or is the screen?. The screen seems phisically undamaged.