Green pixels while gaming and crash game or windows sometimes

Hi im writing in acer comunity because im desperate of this problem again.A month ago when i was playing league of legends my screen suddenly became in green shining pixels and in one moment the game crashed. I run the game again then the windwos crashed.I was verry upset it happens every day usually and only on games not programs or browsers with the exception of program geforce experience the program is in green and red pixels too. Even nvidia and microsoft didnt help me or youtube videos.I was adviced in acer comunity to clean my laptop place thermal phaste and test videocard. i sent my laptop to service and they clean it and place thermal phaste. Also they check my videocard and they said its alright.I play a week whithout problems whithout overheat and increased FPS but today the problem showed again. Iphone service that helped me ago and they said that maeby my chipset is brooken because of the overheating and i need to buy a new one.Im not sure what should i do can someone help me please ?