I am not Nostradamus, so can't tell you for sure what was wrong, but what I think it was wrong from my experience and from what you said about all of this, I think it is like that: because of great variations from high temps(you said was worst temps) when working and low temps from when the laptop was shutdown, all these make a stress on connections between vga and motherboard(you can google about it, are some metal little balls : search 'reballing vga'), I see a lot of laptops on the shop I work, from hardware failure this is most frequent, aprox 80%, most people put the laptop on lap, on covers in bad, so on, so the laptop can't get enough air, or don't clean at least once pe year the cooler (or re-paste, I put my laptop on desk, but I lifted with the helps of 4 cap from cola bottles, so now I can put my hand under him, this reduce the temps a lot, so put more distance between the bottom of laptop and desk , next time)...now, at you, the connectiosn was very fragile because of high difference of high/low temps, when you got down the radiator, you make it more less connected, so now, if it is low temp, the vga it is connected with motherboard, but if the vga start to warm, the metal will expand, and will lost connections(or part of it), so will show you that problem, so I think you did not break something, but you just speed up the breaking process, also you must know that even after re-balling, will not be as new,you will must take more care about temps, and 25% of vga tend to have again same problem in first 3 months after reballing...
