I'll guess you are using Windows Media Player. If so, you need to install updated CODECs. Free CODEC packs are available @ download .com and elsewhere.

However, I strongly suggest you give the free VLC a try. It has the CODECs you need, uses fewer resources than WMP, and is less tempermental. I began using it more and more until last week, when I stopped using WMP altogether.

Som good tips here: http://www.gnutellaforums.com/downlo...ad-issues.html