i have a macbook unibody model A1278 which is late 2008 model, i have opened my macbook and cleaned the fan before but today i tried to open it and clean it as my macbook gets hot and there is always a loud fan noise, but unfortunately 2 of the screws are stuck and they won't turn at all. so what i'm asking is that possible to clean the fan with compressed air without opening the fan? and will it be a useful thing or just a waste of time ? and if somebody know how i can open the stuck screws that would help

thank you