the same problem occurred this morning, computer booted up but no sound.

no problem, thinks I, restart the computer, all will be well, but alas no.

so I went to this thread and read the bits about checking to see if anything was ticked "Mute" on the Volume Control, and there in the bottom left hand corner the box that says "Mute All " was ticked. I unticked it and all was well, but the nagging question remains, how did the box get ticked in the first place ?

I used to be an "X-Files" sceptic, but now I'm not so sure ...

anyway, thanks again to everybody on this thread.