I had all three monitors working last night. Woke up to find that only 2 monitors would display anything! The third is not in a displayport as a hdmi to display port converter is TO DAMN HIGH. So it is in VGA(Monitor side) to DVI-I(Graphics Card side).
Now whenever my 3rd monitor is even just plugged in, the other 2 monitors shut off, and cant do squat, until the third monitor is unplugged. Whenever I press the menu on my third monitor (Samsung) i get a Test Good message top left, sometimes it switches between analog and digital. The menu on the monitor itself is not working fully I think.
(Running a GTX 660TI)
Motherboard: Pegatron Corporation 2ac2
Are you running Windows? If so right click your desktop and click 'Screen resolution'. Do all the displays show up? You should have 3 displays show up
If i connect my third monitor all the monitors go blank, so i cant even see if it does, but i hovered my mouse over the detect button in screen res as i plugged it in, monitors went blank, I clicked detect, and then unplugged the monitor to see that it did not know that their was a third monitor plugged in.