If resetting the smc & pram do not work, it's time to take the computer to an Apple store or an AASP. Whichever is more convenient for you. Diagnostic testing is free. If you do not have Apple Care, you will be responsible for the repairs.
Apply to you? MacBook Pro: Distorted video or no video issues . The affected computers were manufactured between approximately May 2007 and September 2008.