You didn't mention the model or age of the machine, or the Operating System. Or how long the problem has been occurring. This info may help.
Also, have you looked for a newer display driver?
Have you tried System Restore to a date/time prior to when the problem began.
If the system is under warranty you might contact the manufacturer or vendor for support. Regardless of age, the video hardware may be failing. Have you tried connecting it to an alternate monitor to see if the problem persists.
These things may give other Forum members clues to what may be causing the problem.
My laptop ( Toshiba) started to " flicker" like it was going to quit on me.It's only a little over a year old and used 2-3 days a week.
Now the screen looks as if it has been highlighted to "select all" but darker. Blue and grey colored & you can hardly see the pictures and words.
It may flicker to a normal screen on occasion but not long at all.
I'd appreciate any help I can get !