What those it means when a computer has a black screen

Sounds like the graphics card just died. You will need that repaired.

it means that the monitor is not receiving any signal from the cpu, check the cable that goes from the tower (cpu) to the monitor

This means that you have a broken backlight. If your monitor is still under warranty you should call to have it repaired/replaced, or purchase a new monitor.

Right click on your desktop go down list to properties and left click under the screensaver tab click the power tab and turn off the power saver in other words change settings to always on and no hibernation

Time for a new camera, the cost to have it exchanged by Nikon is near the cost to replace.

Have you tried pressing Fn F5? On my system (HP), by computer monitor goes dark when I connect the projector. Pressing (Function) FN F5 toggles the video between Computer Monitor, Projector, or Both.
Check the function settings for your computer. On my Compaq laptop at home, the video function is F4, so there may be different settings for your computer.
Good luck!

my computer power is on and my computer also start quick but the screen of the this moniter start after 15min to 30mins this problem how to solve.

Black screen on your camera when connected to your computer means your cam is on transfer mode and its normal.

my monitor says desact monitor and I dont know what it means.