Laptop Display Remains Black

Laptop flickers at bootup, then display stays black.

Sleep light stays on, then dims in and out right away in front of laptop.

When I move my mouse or hit a key on the keyboard , Screen comes on fine for one or two seconds showing Operating Systems loaded fine. then returns back to black

Laptop works fine on an external display monitor with Operating System.

IS THIS A LOGIC BOARD PROBLEM, SLEEP SENSOR PROBLEM, DISPLAY CABLE PROBLEM ?? PLEASE HELP??

I replaced inverter, inverter cable. Did not replace display data cable .