That means you die.
If you die before you were able to go back in time and kill yourself, you never get the chance to go back in time and kill yourself, and as such, you are alive.
Would that mean that nothing you did would hurt your younger self?
[Edited on 04.24.2012 8:55 PM PDT]
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When you went back in time, you created an alternate reality. You dont exist in this reality anymore (because you killed yourself) but you go on normally in your original reality, Up to the point that you went back.