Can't Unlock Champions

I've been trying to unlock Ezreal for a really long time now and i have more than enough IP for it, but I cannot press the unlock button. I checked with pretty much all the other champions and it says the same thing. Also, when I try to purchase champions from the store it says, "Session Expired" and tells me to restart the game, which I did, heck I even reinstalled it but it still won't let me buy champions. Please help.