Warning: Do not attempt to resolve this paradox on your own. Trust me, you will lose a few years of your life.
You have just discovered a time machine, but there's a catch: every time you go back, your actions cause your grandfather to never exist, making your own birth impossible.
But wait, it gets worse! If you go back and kill your grandfather before he meets your grandmother, you'll never have been born, which means... you'll never have gone back in time and killed your grandfather!
Or, if you go back and save your grandfather, you'll still be alive, but your parents will never have met, which means you'll still never have been born... and so on.
Try to wrap your head around it. Good luck.
Want to try to fix it?