Have you noticed any funny smells coming from it, like ozone or burning insulation? It's possible that it's got a short-circuit or a faulty capacitor. When in doubt, return it. It's not worth risking the chance of a fire.
FYI - there's a reason manufacturers won't repair monitors with faulty electrical components. It's probable you'll get a new one to replace it.
Edit: I should also have mentioned that it's not a good idea to poke around inside the monitor case trying to identify the fault - could result in a very nasty shock and burn.