Disable the JAWS Screen Shade or Narrator developer mode features. If these features are on, your screen will be black to anyone looking at it. Turning off your screen reader(s) should also get rid of the black screen if it's caused by the screen reader.

Make sure your brightness is set to something besides 0. If that doesn't work, It's very possible that your display burned out or has many dead pixels. If it's a laptop, you're most likely out of luck, unless there's a way to replace the display.

Have you tried connecting an external display device to your computer via HDMI, VGA, DVI, or whatever video connector your computer uses? If video works on the external display, your graphics card is working which means it's most likely a problem with your LCD.

If you can't afford to have it fixed, you can probably carry on normally and wirelessly cast your screen to a projector when you need help. The screen reader doesn't care if you have a display device connected since it gets all its information from the operating system directly.

Yeah, my thought is either dead pixels, a blown backlight as was pointed out, or something wonky with drivers. I'm thinking it's one of the first two. Let me know what happens when you connect an external display.

Ask a sighted person to look at the screen, then reboot. Does the screen activate properly during the initial boot process? if so, it's your screenreader / drivers / settings. If not, hardware problem most likely.