Missing WMplug codec, no sound in WMP11 with mpeg video

This was never a problem before, and I’ve google searched and tons of people have this problem with no solution.

At first I couldn’t even play MPEG files in WMP11. I then downloaded the XP Codec Pack from free-codecs.com. From this point now, I can play the video but with no sound. I can play the videos on another computer in my house without a problem and it says it is using WMPlug for the audio codec. I can also play the videos normally in WMP Classic.