|You may have a graphics/display adapter issue in your computer. Equally it may be a psu problem within the monitor; or some part of its signal processing...|
Meanwhile a few simple tests...
Can you confirm if the same situation arises with another monitor connected to computer?
Also if you have another computer available - test the monitor connected to that computer. If the "fault' persists then you have have a monitor problem. If it doesn't produce the fault condition - i.e. monitor works OK - then the problem is within the original computer to which you have the monitor attached?
Equally - if you simply power up the monitor - not connected to "any" computer - does the same "fault" appear?
And if per chance you have another monitor handy, connect that to your computer and see if the situation is present with that replacement monitor?