I don't know. I've spent quite a lot of energy on that myself. The best conclusion I've come to has been: I don't know.
I mean, we probably don't. If determinism is true - and it seems to be - it's hard to fit the traditional concept of free will to being a part of it.
This is all a causal chain reaction that started with the Big Bang by the looks of it, to be honest.
what about quantum mechanics? I thought determinism is dead. Still does not mean there is free will, just a repetition of random events.