Please let there be sound

So, I get an irate phone call from a guy, furious that his "sound card" wasn't working. He was putting together a "very important" presentation and the numerous youtube videos he had embedded in to powerpoint where playing silently.

Automatically I asked (quite reasonably I thought) if he had turned the volume down on the PC or if it had been muted.

"Of course NOT, I am NOT that stupid." was the the reply. (No of course you're not!)

"Ok" I said "Please can you check your speaker connections. Make sure they are plugged in to the correct socket and that they are powered and switched on."