Keyboard or mouse wakes desktop, monitor screen black but it's ON green light is lit. "Input Select DSUB" shows up upper right of screen. Has happened many, many times.

Most recently above happens, exactly but with a variance: Monitor displays an unusable, much darkened desktop image and cycles from this to totally dark, quickly.

-Has used Dell diagnostic and monitor passes along with everything else included in test.

-BIOS ver. 3.3.6. 9/30/16

Help?

Monitor Sceptre X20WG NagaII

Desktop Dell 3650 i3 6100

OS Windows 10 Home