If your parents were killed before you were conceived, you are going to have a hard time travelling.

Regarding you more general time-travel question:

If you want to get technical, there is the no-cloning theorem. It's hard to imagine sending any quantum information back in time without that resulting in two instances of the same quantum state existing at the same time.

Or this:

Let's say that you successfully sent a message back in time. Of course, such a message cannot change events in the past so dramatically that it stops the message from ever being transmitted. Also, you are now living this alternate time line and so you have no clue what alternate history you just over-wrote.

If there was a purpose in sending that message, then you have a problem. Either the purpose was served - leaving you with less reason to send the message. Or the purpose was not served, leaving you with no evidence that the message was sent.

So, in order to be effective and still be recognizable as a time message, the message would have to describe both potential time lines - the one that you want to avoid and the one that you are hoping for - and suggest the action that needs to be taken or avoided. And when that message is resent, it would have the same information but it would be the time line you believe you avoided, the one that you want to preserve, and how you preserved it.

But what kind of convincing evidence would you have that you succeeded? Perhaps the next lottery winner will claim time-travel as his winning strategy.