If the computer is booted normally, the screen is corrupt during BIOS self-test and then turns completely black when Windows runs.
If the Fn key is pressed to do a diagnostic boot, the screen is corrupt at first. When the screen is supposed to turn blue with white text for memory testing etc., the screen is black. When the VGA test starts, the audio tones can be heard. The VGA test falls back to displaying solid colours instead of stripes. At that time the screen actually shows the solid colours, changing from each colour to the next, but no text.
What part needs replacing?
Dell Inspiron 1720, Nvidia graphics adapter, WUXGA screen.