CPU running slow, What's going on and How do I solve it?

I have a Dell Vostro 1500 laptop with windows 7 64bit and core 2 duo T9300 CPU. My computer suddenly ran very slow. I formatted my hard drive and reinstalled a fresh copy of windows 7 and it still would not solve the problem as it normally would. Windows Experience Index used to give my CPU an above 5 rating, now it suddenly drop to a 2.4 My RAM score also drop to 2.9 from above 5, even after formatting and reinstalling OS. please help me out. thank you.