My laptop often suddenly turning off ,,what cause it?

Question

and it always turned off in the middle of burning process and in the middle if I'm playing game.

Answer 1

yeah, thats frequently caused by overheating.  Google "overheating" and "your computer model" for instructions on how to disassemble the parts of your computer you need to in order to get to the fan.  (you have to get to the inside of the fan, and clean all the dust out)

Answer 2

Probably a CPU overheat. It's a failsafe. If the CPU gets to hot it will shutdown before it burns up. Make sure you have nothing blocking your vents. Also make sure your fans are working correctly.  

Answer 3

Sounds like your CPU might be overworking itself, so the failsafe shuts it off.

Also, is your laptop always connected to the power outlet?

I used to leave my laptop connected for days and i noticed it started doing similar things.

Also, laptops do tend to overheat fairly quickly, they aren't really meant to sustain hours of usage. They exists mostly for the mobility factor.