Verified answer

its your screens backlight, time for new monitor

Either your monitor is going out, or you need to adjust your brightness and contrast. You should have some little dials on the bottom of your monitor, or if it's a newer (less than 5 years old) one you should have a menu button or buttons with a sun and a half-moon looking thing. Try adjusting those.

Increase the brightness of the screen on the screen monitor settings (usually there are some buttons on the monitor)

Usually, a monitor has brightness and contrast controls. Refer to your manual to reset the brightness. There should be a "menu" button. Press it, and try to navigate to brightness. Press the "+" sign, or whatever you have, and increase it.

i got a couple of theories

A) your monitor is dieing

B) your black levels are way to high click the buttons on it until you get the contrast

i think it might be A but ive never had this problme so god speed my friend

Do you hear any sound from case ?

One or two beep is good ! You have to check the cable from CPU case to monitor and the power supplies for monitor.

But no beep is bad ! There's some errors on CPU case such as : RAM, display card, CPU, hard disk ....