My 1st suggestion is to reset the monitor settings back to default. If that clears the problem, you can then tweek it back up to more personalised settings. If that don't work............I suspect a fault with the monitor or graphics card. You could remove the graphics card, give the contacts a blow over to remove any dust, put the card back into it's slot ensuring a snug fit and boot up again to check the results.
Is the monitor under warranty ?????