No sound after switching from a Windows Media Audio9

[Zero_]

I recently discovered something. I was trying to watch a trailer for a movie. We'll call it Trailer 1. The video works, and also the sound. It's a MPEG Layer 3 Codec, according to "AVICodec".

Then I switch to Trailer 2, which has a Windows Media Audio 9 Audio codec. The sound and video is working.

Going back to Trailer 1, it appears to have no sound. It happens all the time. It seems I cannot hear sound, or more specifically "MPEG Layer 3" sounds, after watching a video that has Windows Media Audio 9 as it's Sound Codec.

Can anyone help me? I'm a bit of a n00b when it comes to this.