[Jamie89]

I suppose if you go back to kill your grandfather before you were born, then by definition of the scenario where you are in the past, you are already living in a world where it is possible to exist without having been born. And so killing him shouldn't make any difference to you in terms of the 'if he's dead you would never be born' problem. If you catch my drift?

Alternatively if you want to kill your grandfather AND travel through time without igniting the grandfather paradox, you could just travel to last week and kill him (assuming he was alive last week).