Dell Inspiron 1525 HDMI no sound?

Ive searched around Yahoo answers and none of them are useful. My Inspiron is hooked up to my 37 Panasonic Viera by an HDMI cable. No sound comes from the tv except itunes music wich is wierd. for example i cant get any sound from my tv from watching movies or videos from youtube or music from websites such as myspace. Itunes is the only sound coming from my tv. Any help?