i have a similar issue with led lights with two GTX 680 classifieds. My board is a P6X58D Premium ( i know i should have bought an EVGA board i was young and foolish at the time) and a 1200 watt power supply. Both cards in either slots as singles or Sli no matter how i switch them around the lights will go out as soon as a game leaves the title screen. It will freeze, black screen and i'll have to restart. From left to right the way the cards sit the machine, it's far left and the next two. i can search the web or watch youtube no problem. i also sometimes get the message to "please power down and connect the pcie power cables". i put an 470 in it and it runs like a champ play for hours no problems. i have already reinstalled my operating system new drivers and all that good stuff. Cpu and memory pass Intel ETU. This machine has run well in the passed. Thanks for you help.