Fresh install of LOL after a few years Hiatus, game wont load.

EDIT: Thanks very much for all the help, it turns out that league wont work if you use RivaTurner because of the anti-cheat algorithm. Now works after uninstalling the program.

Not really sure what to do. Turned off firewall, but every time I get into champion select no problem, then when I load into the game, I cant even see the loading screen, instead hit with an error message "A critical error has occurred and the process must be terminated". I've been looking around for a solution and can't find one, any help would be greatly appreciated.