My Laptop seems to have lost its sound system, Bottom right the speaker shows a red cross and there is a message box comes up :-"No Audio output device is installed". in Device manager there is nothing showing for sound - I have tried system restore with no joy, any suggestions before I reset the whole shooting match?

Try reinstalling the audio drivers

Just tried that - no joy:(

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.

Like the Belarc - useful tool, shows "Multimedia - non detected" which should be wrong! Where do I go from here though?

Well, it's a double confirmation that there is no audio device connected to the machine, I would think along the lines of a physical disconnection, maybe look at something becoming unseated from the motherboard - cables, etc. What lappy is it?

Most strange, On starting it up again all seems back to normal (yes I did do a restart after reinstalling the drivers), hopefully not going to reappear.

You might want to find out what has happened there. Click start, then right click my computer, select manage from the dialogue box, then select event viewer then look through the log for both system & application - see if anything relevant comes up as either an error or a warning.