PROBLEM: Black screen of death on a Lenovo y580 (or probably most of the ideapad Y series since they all use similar bios software) after changing the setting for which video source gets priority (default is "SG").   SOLUTION: Rather than using the vast array of options that rarely work for anyone like heating up your video card by blocking the fan on a pillow for 20 minutes at a time until it "decides" to start working again - after much research I found the solution for setting the m