can't start minecraft after reinstalling

I had the "bad packet id" bug, so I made a backup of my worlds in a different folder, then reinstalled minecraft. when I tried to run minecraft, I opened the launcher, and pushed "play", but it crashed and said that it "couldn't unpack natives". I tried many times different ways, but each time it crashed from a different bug... PLEASE HELP ME!!! I have a youtube channel and I plan to get money from it for a job, but I can't do that without this fixed!!!