Game unplayable

Hi guys, i just purchased the Mass Effect trilogy,and i started playing the second one,because i have already finished the first from other sources.After i played like 15-20hours, my game started lagging,it just works 2-3 seconds,after it starts lagging again,its unplayable.I tried repair,uninstall, even changing the graphic settings,nothing happens.Maybe i have messed with the gamersettings.ini to much,if you could possibly send me the default one that would be nice.And the thing is,whenever i change settings from the MassEffect2config, the game wont start,and i have to reinstall it,so i cant really mess around that much with the config! Please help!