First check your cable connections, make sure you don't have a loose or damaged connection. Was the screen flickering or was the monitor actually switching from ON to STANDBY and then ON again and repeat? Maybe test the monitor in another system to make sure your monitor isn't dying. Or try a different monitor with your setup.
Did you ever figure out the problem? I may know what's causing it. Sometime's graphics cards wont mesh with all the pins inside the slot, particularly the one's on the far end due to the card or pins being slightly bent. This in turn will cause your monitor to turn off and on randomly as i've ran into this issue a couple of times on fresh builds. Remove the card and inspect the pins on both the card and slot to make sure they are all in line and intact. Hope this helps.