Pc Sound...help!

[sddsddean]

Don't know what I've done!!

I have got no audio on youtube and some games(simulators). Sound is working fine on music files and game pages on the net, so the hardware is fine. It seems to be anything that is sort of video related. I'm guessing I've accidentally 'hit' a button, but no idea where. Anyone any ideas?

[sddsddean]

So you're a winner too Togo!