LoL [Client} Opens, sits, closes.

[Client] I recently had my computer wiped, and updated to OS X Yosemite (10.10). Now when I downloaded the new League client I dropped it off in my applications folder and then opened LoL from there. However when I open it now, it will sit for about a minute before a window pops up and says "Another instance of this launcher is already running, do you want to close it?". My options are "Okay" and "Cancel". Cancel just immediately closes the app, where as if I click okay the app will run for another two minutes before closing without any warning.

I don't even have LoL fully installed/updated and I never see two of them running so I'm not sure how it's possible. Any help?