Tried scanning for hardware changes in device manager? I would think that if previously working audio has simply disappeared, then the device has become physically disconnected from the motherboard, but then it's a laptop, so onboard audio is most likely?
Try running belarc system advisor - that will tell you exactly what your machine is made up from, in hardware & software terms, not a solution to your problem, but a reasonable place to start.
Also, have you tried googling audio problems for your specific model of lappy? There could be a common issue specific to the model.