MacBook Pro 15 inch (mid 2009)either starts up and turns right off or gets stuck at grey screen with spinning gear.

Soy MBP either starts up, chimes, and turns right of when it gets to the first grey screen with the apple logo, or turns on, chimes, gets to the grey screen w the apple logo and spinning gear and just gets stuck.A friend who is familiar with apples have me instructions to do an smc reset, which seemed to do nothing, started up then just turned right off at first grey screen. Also tried the pram reset, and when I turned it back on, I am stuck at the grey screen with spinning gear for almost 20 mins so far. Any thoughts before I buy a new hard drive? I was running osx 10.5.8 if that helps. Thanks!