You likely have a LCD set there which may likely use a back light inside to light the image, get the room as dark as you can and with a flashlight illuminate the screen from a angle, with set on if you can see the faint image on the screen of the program you have a Backlight issue'

1. Voltage not there or not being switched on for backlight.

2. Actual back light bad.

If the image can be seen with a flashlight one of the above is the issue and your "picture will appear very faintly" also suggests this.