You'd ideally need a card with more than one output like Airox said; likely a 4 or above. It is also possible the card doesn't have the power from the Motherboard to send out the controls to two monitors at the same time - hence the Motherboard runs out and shuts down.
A Knight is sworn to Honour. His heart knows only Virtue. His blade defends the helpless. His might upholds the Weak. His word speaks only truth. His wrath undoes the Wicked.