No Sound on MacBook

[jump79]

Since last night, the sound option on my macbook hasn't been working, I've tried restarting it and it initially makes the startup sound but after that if I try to play a video/ music file, it just goes mute?? I looked at system preferences and for the 'output' option, it says 'selected device has no output controls' (its on full vol bar though)...
When I press F4 or F5 to control the volume, nothing happens, it always stays on full bar and this "∅" sign pops up too (never seen it before!)....

Please help, any tips appreciated
Thanks

[fo3nix]

Installed anything since last night?

Click the apple logo, then 'about this mac', then 'more info...', and then click that 'audio (built in)' item to the left -- what does it say there?

Even better would be once you're in that window to go file->print, and choose 'save as pdf', then upload the pdf to somewhere so we can see it here.

[fo3nix]

But before you do any of that, try plugging your headphones (or speakers) in, and then does the sound play?

Possible solution here:
http://docs.info.apple.com/article.html?artnum =300832

Discussion here:
http://discussions.apple.com/thread.jspa?messa geID=2117797