My Dell Inspiron 15 7000 used to run games at a solid FPS of 60 24/7, but that has changed. It suffers from sudden frame drops and low fps of 30-40 in all games. For example, it used to run Shadow of Mordor maxed out at a constant 60 fps, but now it runs at 45 with lowered settings, and suffers from frame drops.
Unistall and reinstall the latest geforce drivers. Secondly clear %temp% files. Third check for any broken DLLs. Fourth reinstall directx 11. Fifth check your hardware like fans working properly or not. Hope this would help you out!!