Out of the dozens of \'monitor had to be returned\' google results I got with your problem, ONE guy had fixed his screen by opening it up, finding a wire that was shorting out with some power component running to the panel. Fixed it by separating the wire.
That said, you probably don\'t have the exact same problem, probably don\'t want to be opening up your monitor. Just *find* the box and exchange it. If you don\'t have the reciept (which would be dumb, if you have a return/replacement program), then go and ask the store for another copy of the reciept, assuming you put yourself into the computer when you bought it. If not, you are up shit creek.