I am unsure what is causing this issue, however, I do know, that if I play any steam games (all of which are pretty much resource intensive) it is a sure fire way to recreate the issue, however, this is not the only reason for the issue, as it appears to happen all the time, for no apparent reason, my guess is that this issue is mostly something to do with the wake/sleep or the switching of the onboard Intel HD 4000 Graphics to the Nvidia Graphics. Anyways, my Mac will apparently shutdown, and boot back up, however, the monitor, backlight, and apple logo lid light, all stop working. Doesn't matter what I do, nothing will get them to work. Everything else works perfectly. After some time, I was able to figure out how to get the monitor, backlight, and apple logo lid light to function normally again. The process for this is as follows: Step #01: Shut the MacBook down via holding the power button until it powers off. Step #02: Reset the SMC as well as the PRAM, after which, allow the Mac to boot back up. Now, the screen will momentarily seem to start to work again because sometimes, after resetting the PRAM the backlight will come back on, but most of the time it will turn right back off. Step #03: After giving the macbook a few minutes to boot up and get to where we assume the log in screen is. After this happens, hold the power button down for a few seconds, only long enough to send the macbook into "sleep", you will know this is the case because the backlit keyboard lights will shut off. After this happens, without pressing any buttons or touching the track pad, simply shut the macbook's lid and leave the macbook alone for approximately 10 minutes or so. Step #04: After approximately 10 minutes or so, open the macbook lid up and move your finger across the track pad and press a few keys, and if all goes well the mac should wake from "sleep" and with any luck the screen will come back on and begin to function normally again, at least until the next time this issue happens. Now, it should be noted that when the screen is in this state, and not functioning, nothing will get it back to working, except the above mentioned methods. I have tried to boot it into recover, safe mode, even tried booting it up while holding option key and trying to boot into windows via boot camp, nothing works. I have also tried to wipe the mac and reinstall mac os x, however the first attempt didn't seem to do anything because the screen went out twice during the installation, however, afterwards, it went about 2 weeks without any issues and then the issues starting happening again. So, any help would be greatly appreciated, feel free to post here or email me at email@example.com because I am going out of my mind trying to resolve this issue. I had absolutely no problems at all until after updating to Yosemite. And even then the issues didn't happen until about a month and a half ago.