No sound on my macbook pro

Try doing a Parameter RAM reset - hold down apple/option/p/r keys at start up and wait for three chimes before releasing the keys.

Hi "someone help me,"

Sorry to hear we're having sound issues. What happens if you plugin some headphones into the jack? Are you getting any audio output? How about if you make a new user account, any change there?

The fact that you're getting sound on POST indicates that on a firmware level the computer is detecting the appropriate sound drivers. We might be looking at an Archive & Install of the OS based on how the first couple of questions asked above turn out.

Let's try the following:

1.) Insert the OS X Installation DVD that came with your computer, restart the computer and hold the "C" key on startup. It'll take a few extra minutes on the Apple logo with spinning gear and then it'll greet you with the "Welcome to Mac OS X Installer."

2.) Click on the initial continue arrow, agree to the license and then immediately go to the top menu bar. Click on Utilities and then go to System Profiler. Under the Audio listing, does it detect any audio hardware? If so, I'd proceed with the Archive & Install, if not I'd consider bringing the unit into an Apple Retail Store or Authorized Service Provider for further diagnostics.

Reason being... when you're booted off that disc you're taking your OS out of the equation as you're running off the CD in sort of a "default" state. It might be worth it to do the A&I regardless. Just be aware that after it's done you'll need to re-run all of your software updates as well as install any 3rd party applications.