GPU Glitches and Failure
I had the same problem a couple of months ago...
I read all I could about it on the net and came to the conclusion that (in my case) it would be an expensive fix.
What helped was an app that allowed me to force the use of my chosen GFX card - Discrete or Integrated.
Despite that the problem got worse over the next couple of weeks until once powered down I was unable to turn back on my MBP (Early 2011 17" 2.3Ghz i7).
I started looking for a replacement but while doing so found 2 people who had the same problem and had tried a rather drastic repair.
Thinking I had not much to lose I tried the same thing....
The problem was identified as (possibly) being caused by faulty solder joints around the GFX chip - heat being the culprit. My MPB has been used intensively since I bought it (Cinema 4D, Avid, FCP, After Effects, Photoshop... often simultaneously, with the CPUs running at 97 - 98 C for hours (even days) at a time.
The cure... (maybe)... was to strip the MPB down to it's component parts and remove the logic board. Then I did what the other guys had suggested......
I baked it in the oven for 8 mins at 200 C !
After cooling and reassembling it booted up and ran like new
That was about 6 weeks ago and I've had no recurrence of the problem.
I understand the reasoning behind the solution - the intense heat my MPB had undergone had possibly affected the joints around the GPU connections and the baking had re-flowed the solder, remaking the connections, but it was a drastic solution and one I tried only after realising that it would cost hundreds to have it repaired by Apple which probably wasn't cost effective (being almost 3 years old).
Being so risky I could not recommend that anyone else try this unless they are ready to bin their laptop and have nothing to lose. All I can say is that several weeks ago I had an MPB that wouldn't boot up after having the problems described in this thread... now I have one that is working just as hard as it ever did and is once again cooking my legs as I work on it !
If you do decide that this might be a solution for you then please search the net for advice - reflowing solder, MacBook Pro, GFX etc etc...
Despite being immensely satisfied with having repaired it in this way I'm hugely disappointed in having a (relatively widespread) defect like this in an Apple product that Apple themselves shy away from.
I'm just keeping my fingers crossed that my "Medium Rare MBP" keeps cooking for a while longer.§
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Forgot to say that while it was apart I found a huge amount of debris in the fans... can't have helped the cooling !