Remove all added accessories, as well as the added second screen - in short, leave only the essentials.
Make sure you have the correct disply driver and also that all the connections are good. Remember, that the latest driver is not always the best. If possible, use drivers recommended by the computer producer and do not replace them with any updated generic drivers as long as the producer recommends.
Of course you can buy a new display, but my personal opinion is that this is not a disply problem and replacing display also is not the solution. But this is only my opinion.
Maybe you want to tell which computer and display it is and when and how the problem occurred?