Can't select champions/won't connect to champ select

Sometimes when I queue up for ranked, I hit accept and get into the champion selection screen, at this point either my game freezes or when I click to select a champion the button presses but it won't select the champion and I will be forced to dodge, I have an almost new high end computer (about 3 months old), a perfect internet connection and can't find anything that could be causing the problem, waiting for leaverbusters and losing lp because of this is rather annoying so if you could find a fix to this that would be great.