Macbook PRO 2009 running extremely slow all of a sudden

Hello, I have been encountering recent problems regarding my macbook pro 15" from 2009. All of a sudden it became extremely slow and spinning beach ball every time I click something. It used to be very fast it's as if something happened over night. I have already tried re formatting the whole computer and installed a new os x. I verified the hard drive that it's okay and I have already reset the pram. Would love some help please and thank you. Specs for my laptop are: 2.8GHz Intel core 2 duo, 500GB HD, 8GB Ram and it's from 2009. No recent applications were installed.