Sound doesn't work on Macbook Air!

So, my uncle recently gave me a macbook air running snow leopard 10.6.8 and the problem is the sound doesn't work. We originally thought it was the sound wire, but if that were the case the sound icon would be ghosted (or so i've been told) and i still can raise or lower the volume, but no sound comes out. If i plug in headphones, still no sounds. The internal mic also doesn't work, and when i go to sound settings the internal mic and speakers don't show. How can i fix this problem and what is wrong?