Hi Mac users, Problem: My MacBook Air shuts down spontaneously after a maximum use of 2 minutes, sometimes even while its booting up. It doesn't go to sleep mode, from one second to another black screen and my laptop is off. Opinion from repair store: In a repair store they told me the mainboard has to be changed out, and it's not worth the price for this model. Solution: I thought it could have to do something with overheating (since my MacBook Pro 2011 had this overheating problem with the graphic card). I tried putting the MacBook Air on some freezing bag and started it... and what a surprise... it runs perfect now for already 2 hours... so the problem is definitely "overheating", but I have no idea which hardware is overheating... is it really necessary to change the main board? And tips, suggestions, advices,...?! Model: MacBook Air 11'' Mid-2012 1.7GHz Intel Core i5 Memory 8 GB 1600 MHz DDR3 Graphics Intel HD Graphics 4000 512 MB Software OS X 10.8.5 I would really appreciate your help!!! Thanks in advance!