I had this problem, sometimes when i wanted to download a file even if the file was very popular it was downloading at a very low speed or waiting to start. So what I did was selected the file and pressed the pause button and after that immediately pressed the resume botton. And the file started downloading at my full download cap. If it doesn't work on your first try, do it a couple of more times. I am not sure if it will work for you though. Try it and let me know.