Like F22 said, that is the store display attract mode popping up. If it is still under warranty i would get it checked out as it sounds like the logic board is going bad.
As i had the same thing happen to my samsung syncmaster the store mode would pop up on and off and when i took it in for repair the reapirman said it was the logic board and would cost $125.00 for the logic board and and $75.00 for the repair i told him never mind brought it back home and tossed it in the trash. I did lose out on the $25.00 dollar diagnostic fee though.
Not saying that is what is happening to yours just something to consider.
Try this before going to bed unplug it from the wall and your monitor cable and let it sit over night. It might reset itself and have no more problems with it. Also look at your monitor settings and see if store mode has been enabled. Maybe someone turned it on to play a joke on you.