In reply to marky:
Can you try another monitor with the laptop to prove the output? It could be a GPU issue (hardware or driver), but that sounds like quite the obscure issue if it resolves itself some time after plugging the display in. If you have access to another, it might also be worth swapping the adaptor out to see if that changes anything.
If it doesn't happen with another source, I would rule out the display being the problem.