CLient making me patch on every start up

So the past two weeks, everytime i start up league, i get the "we have reinstalled a previous patch blah blah" notification, then league proceeds to repatch the client, which takes up to 2 hours sometimes, i uninstalled completely, reinstalled(which took over a day to do due to the file being absolutely huge) and i got an error 0xc0000005 or something last night, but now that has gone away and the client starts, but im still having to patch every single time i start up. does anyone know the cause of this and/or a fix ? thanks