Macbook(Intel) OS X 10.5.8 sound stopped working
The same problem occurred on my MacBook(intel) and OS 10.6.3. I tried the manipulations as described and found that this a mechanical problem.
If you look inside the earphone connection hole you see in the front two copper-coloured connections you can push a little to the left and right. These are not the ones you want.
If you look deeper you see in the centre rear a point and to the right a similar pushable connection as in the front. This is the one you need. Push this one back and you're in business.
It worked like a charm.