[CLIENT] Computer Crashes when im in a party lobby, deletes all my settings including item sets?

I got on to play a game with a few friends of mine, and while i was in a party lobby waiting to start the game, my computer crashed and i had to restart it. When i booted back up and reopened League, I noticed my username was no longer remembered, and all my client settings had been reset to defaults and all of my item sets were deleted! Can anyone explain why this happened to me? This has never happened before after a crash.