I can't move my character, or cast spells. (It's not a connection problem, or my mouse)

So for some reason, every now and then, I get into game and ever thing looks fine. I go into my respective lane and start farming and trying to help the team. I decide to engage on the enemy champion since he was in a bad position, but then I couldn't move my character, or cast any spells. It wasn't a connection problem, because the game was still moving and I could still see my team move without lag, and still chat with my team. At this point, I am standing still like an idiot getting pelted by minions while the enemy champion kills me with ease. So I tried researching this problem. I figured out so far that other people used to have (and probably still have) this same problem. It's not my mouse, because I can still right click and try to move, but my character won't. Champ won't move, or able to cast spells. So I am very confused on what to do. I can now only assume that this is a bug, or something. I die at least one-two times because of this problem, and It's very annoying. Sometimes it happens, sometimes it doesn't. Sometimes it happens once, and sometimes it happens frequently. Please help, I don't know what to do or what this problem is.

Thanks.

Your average league player, KyotoKhan