Recently downloaded but client keeps crashing.

A friend is trying to get me into League but whenever I go to launch a game the client crashes. I've run the hextech repair thing, uninstalled and re-installed, allowed it through firewalls and so on. I'm able to play Dota and Heroes of the storm and never had this problem. I keep trying to do AI matches but when I click the 'confirm' button I instantly get a crash report. Anyone knows what's going on?
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