So, how old machine it is? What virus scan you use?

@pastgone (View Post)
Did you check the Graphics Card fan?

@UBERNESS do that definatly its probably overheating possibly not the gc fans though you might have a faulty motherboard. 

Maybe it just needs to be cleaned.

@IronRhino (View Post)
That's possible. Maybe graphics card is broken, or if you have bought new screen, driver might be unsuitable, so you have to change it.

Buy a Mac.