fps Problem with my Dell 15 7559 960M

Hey! New here.. My Dell Inspiron 15 7559 - i7 6700HQ - 8GB - GTX 960M is not running games as it used to. I only play dota 2, and used to play Full graphics, 1080p at 60fps, now I can barely play at 40fps with everything in low at 1080p. Is it possible that my 960M is not working as expected? or that my integrated graphics are running instead of the 960M? Any help to troubleshoot this issue is VERY welcome. Thanks!