Why doesn't my screen display a video, What should i do if my screen is dark – Sony VAIO VPCZ12 SERIES User Manual

VPCZ12DGX, VPCZ12CGX, VPCZ124GX, VPCZ12BGX, VPCZ12NGX, VPCZ12EGX, VPCZ12LGX, VPCZ12MGX, VPCZ122GX, VPCZ127GX, VPCZ1290X, VPCZ128GX, VPCZ125GX, VPCZ12GGX, VPCZ12JHX, VPCZ12AHX, VPCZ12HGX