Mouse randomly not responsive

I've been having an issue lately where my mouse just stops responding in game. The game still runs normally, its just I can't use my mouse. What's weird is that the normal windows arrow comes up instead, and I can move that around, its just I can't do anything in game. This problem is unique to league; it doesn't happen in any other game. My specs are intel i3 3.5ghz radeon R7 260x 4GB ram Win 7
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