Why doesn't my screen display a video, What should i do if my screen is dark – Sony VGN-AR870NA User Manual

VGN-AR760U, VGN-AR890U, VGN-AR770NC, VGN-AR710E, VGN-AR825E, VGN-AR870ND, VGN-AR730E, VGN-AR840E, VGN-AR770ND, VGN-AR720E, VGN-AR770U, VGN-AR820E, VGN-AR750E, VGN-AR870NB, VGN-AR830E, VGN-AR770NB, VGN-AR870NC, VGN-AR790U, VGN-AR870, VGN-AR810E, VGN-AR705E, VGN-AR850E, VGN-AR770E, VGN-AR770, VGN-AR770NA