New MPB...suddenly no sound?

Hello, recent switcher here, love the Mac! I've run into one problem: I now don't have any sound, noticed it when trying to watch video in Safari, or music in iTunes... I'm running with a cinema display, and everything else seems to be perfect. Checked all settings I could find, to no avail. Might this be something simple a Mac newby might have overlooked? I installed Office 2011 today, but don't know whether this condition existed prior.

Silly question but just in case, have you checked the speaker button (F10) on the keyboard? Probably won't be that but just in case....

Can you see a red light when you look in the headphone jack?

Take your headphones and plug them in and out a few times untill it turns off.
I took a toothpick to mine and just sort of tickled the inside of the jack to reset the optical out.

It happens, but by the reports I've seen, most are similar to mine... e.g. it's been a one time occurence in my now 4 yr old MBP.

ok, the sound came back when I ran the MBP without the cinema display, and when I reconnected to it, it was fine...wierd!
Kinda scary--like a Windows "now you see it now you don't" peripheral problem...