I'm looking for a sci-fi book I read a while ago. I have the impression it was reasonably old. Anyway, so the opening sequence is a crying child refusing to get on a spacecraft and his Mum and Dad get on anyway and it blows up and kills them. So the kid grows up desperately trying to find a way to go back in time and warn them. He discovers a button or a machine and tries to use it, and the actual main character shows up and begs him not to. He does anyway and ends up stuck as a passenger inside his own body, unable to do anything at all and has to watch them die again and go through the loop of his life forever and ever. Thanks for any help!