Then open the file, copy the 1st one if you play on EUNE and the 2nd one if you play on EUW.
Then find you League of Legends folder < RADS < System and open the System.cfg with a program which allows you to open .cfg. Delete anything if you have inside there and paste the thing you copied from the previous file in there. Save and close.
You can now open League of Legends and hopefully play! ^^ Glad I could help!