Screen will not show picture/remains black. First time this happened tried to turn off-on through switch with no results but after unplugging and hooking back up the screen showed a picture; computer main page. Second time; about a month later and numerous on-off sucessses,same thing happened but his time unable to get picture. The difference this time is that after unplugging/rehooking the on-off indicator flashes for serveral minutes, turns solid green but still no picture. Any ideas?