Time machine!!!!

Nothing! I would be very tempted to change many things in my past; but there are too many unforeseen consequences that may result. For better or worse, I think I would just accept the past and just look forward. BTW, have you seen the movie, "The Butterfly Effect?"? It's a very entertaining look at just this topic (although there's really no time machine involved; the main character has the ability to travel in time naturally). Check it out.