New version WMP plays video but not sound on some files

I have upgraded from my previous Windows Media Player to Windows Media
Player 11 (specifically 11.0.5721.5280).

Unfortunately, I cannot get this version to do everything that my
previous version did.

While I have no problem with video, I cannot get WMP 11 to play the
audio on some of my files.

The new WMP 11 play Windows sound on SOME of the Windows Media
Audio/Video File that I have converted from FLV files on websites. They
are, for example, movie trailers, television scenes, etc...

Files that I converted to "Video Clips" or to "Movie Clips" all seem to
play the sound as well as the video but only some of the Windows Media
Audio/Video File from hard drive plays on WMP 11. They all played on my
previous version of Windows Media Player.

All play video, but not all play sound.

I can find no pattern as to which FLV files that I converted to Windows
Media Audio/Video Files will play sound as well as video on the new
version of WMP and which will not. Since I created many of the files in
the past I cannot recall if the difference depends on which program I
used to make the conversion.

So my question is, does anyone know of a way to get the new WMP 11 to
play sound (as well as video) on all the FLV files that I converted to
Windows Media Audio/Video File?