Dell Vostro 3500 lagging and unstable fps

right now i don't really know what happen with my laptop because whenever i play anygame it keep shuttering and fps dropped at first i try to lower the cpu performance from 100% to 95% and it worked for a while but then the issue come back then i try others way like reinstall the Nvidia driver since this laptop use GPU MX330 and try the performance setting but it doesn't work, i try to upgrade this pc to dual channel 16gb Ram and using a coolpad but the problem still there. I think the problem may be from the Nvidia GPU because when i disable it and use the onboard GPU it's work completely fine with 60fps all time with no fps drop if anyone have a solution for me please tell me i don't know what to do now

i forgot to tell you that i even clean the fan so the thermal throttling issue will not happen