Think that's called the Grandfather paradox.
If you're referring to my time travelling to the past and fucking everything up comment then yes, it's the grandfather paradox. If you went back in time and shot your grandfather (and killed him), you'd have never been born so you couldn't have gone back in time to shoot him.
Think Hawkings said he reckoned there would be some kind of force field that would prevent you going back in time to stop that shit going down, or something like that. Though some people think Hawkings is talking shit and it is possible with alternate timelines and the like.