I have the same monitor, the same video card AND THE SAME PROBLEM.
Looks like its something about the way the on/off switch works.
I have already returned the monitor and got a new one, but the problem persists. And it not happened on the store (after 40 minutes connected at a store's PC), and my old Samsung monitor (an LCD 19" one) works OK too.
I will just sell this and buy another with regular switch.