Alienware 15 R2

Hello im looking for help, i own this computer since like 2016 and its been through some stuff. For about a year now ive been getting these crashes whenever i dont use the computer, weird. i was in a service shop in it they changed the thermal paste and it didnt do much with the crashes. still...

Hey guys so i want to know what exactly is bottleneck? Example : a cpu can bottleneck the game or gpu ... How so? Like the game will slow down? Or stuttering or low fps Thanks for help