ask him if he's ever taken apart the laptop, (or even just opened up one of the panels for RAM) because I had a laptop where the speakers were under the palm rest, but to add ram or anything you would have to lift out the keyboard and open it up that way, but if you weren't careful you could easily disconnect the speaker wires. If you open it up, and everything is connected properly and you still don't get sound, maybe you could just modify the wiring in the laptop and solder directly to the port for the external speaker.
Now I've just had another thought:
There is usually a switch inside external connector, if something is messing up that switch, that could be whats causing the internal speakers to not work. Try plugging something in to the external port and jiggling the connector around a little bit and unplugging it again, and try a few times see if that could do it. I've had that happen to me before (not on a laptop though, but other stuff)
at least you can get sound out, so I don't think theres anything wrong w/ the actual sound interface. I think it might just be a hardware problem w/ the speaker configuration inside the laptop.
good luck