Can't think of anything I'd prevent happening, so I'll just say what I'd do if I was bestowed a time machine
I wanna go and say hello to the dinosaurs! Yayayayaya. But seriously, I would if I could so it safely. And she one of Shakespeare's plays, preferably Romeo and Juliet. See the coronation of Queen Elizabeth II....and I'll add more when I think about it. Actually, it might sound bad but I'd like to hear one of Hitler's speeches, see how much of a dictator he actually was. I dunno.