There is an MPG file that when I open it in Gspot, the Aud does not render and the Vid does not render, but if I hit the MS A/V, the audio and video play fine. Why?

Each time I have used Gspot to try to diagnose a problem, it always shows the audio and video codecs as being installed, yet there is a problem, or I would not be trying to troubleshoot. Why?

How can I better learn to use Gspot? I tried AVIcodec. When I loaded the file that I am trying to play (MPEG2 with 48Khz LPCM audio), it reported that LPCM is not yet supported. Huh?

Understand that the file (now) plays, even though there is some tearing and some random pixelization on the right side of the screen that is not present when I play the file on another computer. The problem computer reports using the CyberLink Video/SP Decoder (PDVD7) while the good computer reports using AverMedia MPEG Decoder. Is it possible to install the Avermedia codec on the problem machine without installing Avermedia? How?