If this is an LCD monitor – flat screen – the problem could be the backlight. When it fails, the monitor is dark, but sends no problem signals back to the computer. Shine a flashlight on the screen to see if you can make out anything. Once the backlight is gone, if it’s a desktop monitor, just junk it and buy a new one. Repairs are too expensive, and LED backlights are starting to go into production. They have a longer lifespan. If the problem is an ordinary CRT monitor – send it to recycling. It’s not worth fixing, either, but check your video card with another monitor to make sure it’s working first.