Computer monitor out of range is being flashed on screen

Monitor is not recognizing the resolution settings that are currently set on the computer.
It is probably sett too high.
You will have to lower the computer resolution.
If it is a laptop, you should be able to do this using the laptops screen.
If it is a desktop computer, you either have to use a different screen to reset the resolution.
or
Sometimes restarting the computer while the screen is on will reset the video.
If that doesn't work, try starting the computer in safe mode by tapping the F8 key while it is being started. This will keep the resolution low enough to see it on the monitor and you can adjust the resolution there in the display properties