Acer Asp 6736G problem

i have an Acer Asp 6736G
it's working smoothly, but the problem is it get turned off instantly when i'm using it, i don't know what's the problem, sometimes when i just turned it on 10 secs after that it get off by itself but sometime it can hold up to 1 hour
it's not because it's hot, because usually it get turned off right after i turned it on
i tried to open it and apply some thermal paste (cause the thermal paste is already dried up) but it's not working at all, it still have the same problem
i tried bringing it to an acer service center but they said "the motherboard is the problem so u should buy a new one" (like hell!)..
so any suggestion?

 

Yes. Its the better option.

 

Another possibility is a bad memory module. If you have 2 modules, try removing one module at a time and try to boot.