the reason = any electronic parts which includes the mobo has a lot of components especially the microprocessor/microchip. the only holding the chips on that motherboard is the glue+solder. after sometime or even heavy multitasking to the point of high temp 80-90C this bonding could fracture/weak until one of its leg/pin came off from the board = no more contact. this will result for no boot up, beep, other weird error. this happen several times to my macbook air 2011. Under high intensive task or even gaming for Roblox i notice the CPU temp raised up to 90-95C. After prolonged usage at this temp, the macbook failed to ON like beeping, sometimes only Fan running but no boot. It happened 2-3 times already I noticed. The solution i baked the mother board in the oven, since it is no longer under warranty I dont mind at all doing it. It works flawlessly after the baking, no replacement parts whatsoever during the process. totally bake the motherboard. The unit then able to boot and can use like normal. Now I learn my lession, macbook air or maybe other macbook, you need to ensure the CPU temp never hit 80 and above for a very long time.

Not only motherboard, I also baked my old GTX 9800++ graphic cards after it has some weird error artifact on the screen. it restore my card well till today