The monitor goes on but no picture. when i turn

The monitor goes on but no picture. when i turn it on the screen turns blue and then black continuosly.
I have the same problem. When I first turn on the monitor, a full screen of thin, colored, parallel lines appears. The screen flashes like it's trying to display the image, but then it flashes to the blue screen. Audio comes through fine. This just started happening. Set is three years old.