It's all the power saving rubbish in the monitor menu, there is like 2 places on a samsung monitor to turn all that rubbish off. It can even cause the motherboards to throw up errors related to vga when all that stuff is on, the samsung monitors seem to go into a deep sleep mode and don't wake up again from desktop sleep mode or a starting up the pc and when you get the post errors then.
Turn off the eco stuff and should be fine then and will go into normal sleep mode and not the deep sleep that causes these issues. Remember at least 2 places to turn that stuff off and then turn the monitor off and back on to make sure it takes. If the blue led on the front is not flashing it means its in a deep sleep, flashing means normal sleep and will work fine from startup to desktop sleep in windows.