League of legends minconfig fps drop and windowed

So couple weeks ago my pc runned league efficiently without any problems.However couple days ago a problem with my firewall occured and i couldnt run league anymore.I sort it out and joined a game but then after jumping into the game i had fps drop and the game couldnt be played at full screen.Plus i had these instructions: How to use the MinConfig settings This WILL replace your current in-game settings

1. Log into your League of Legends account.
2. Go to your "Config" folder (default location: C:\Riot Games\League of Legends\Config)
3. Highlight, drag, and drop the following files into your "Config" folder: game.cfg and PersistedSettings.json
4. If a "Copy File" window pops up, click "Copy and Replace" for both conflicts. If not, skip to Step 5.
5. Start a Custom Game by yourself. You should have the minimum configuration settings.

Which i followed and now i can play league only in windowed mode.If anyone knows what has caused all of this and can help please respond