I agree with iamyourmom. Try to check the parts of your motherboard and see if they are free from dust, especially the video card this is sometimes the reason your computer restarts while in the middle of the game. This happens sometimes here in our computers in our shop while they are in a middle of a game let's say DOTA the pc will just restart. What you need to do is try cleaning your video card with a paint brush or something. Oh and btw im using a cleaner here its called WD-40 it stops squeaks, moisture, loosens rusted parts, and it frees sticky mechanisms.