Not responding

When i try to open the game, it just gets stuck on downloading like 1/8 th of the downloading bar threw. Also when i try to play mod packs from curse it wont work, it just says "preparing" for ever and the goes to not responding. and io didnt give permission for this update on my computer. Additionally, when i go to chang the version, you have removed the option to change the version and it forces me to stay on the version that was downloaded for me 2.0.1 or whatever.