There are alot variables when burning a disk. If possible always use slowest burning speed when burning (less errors on old dvd burners)(its not an option in Videopad).
It seams like the burner software is having to do to much computations while it is burning so it left out the audio.
Since you already have a wmv copy on your computer...
Here is something to try...
Load that file into Videopad and drag it into sequencer. This will allow the save video button.
Click on that button then click on disc. Then click make dvd movie button, for burner setting use image file not hardware burner.
Click on advanced button and use 9000 bitrate and 320 audio bit rate.
Last click create. When done you will have an iso file.
When Videopad finishes in desktop folder check file size of new iso(right click on file then click properties). It has to be less then 4.7 gigs or you will have to remake the iso after splitting the wmv into two videos.
Burn this using trial of poweriso.
If this works then it was the problem was as described above.
If this still doesn't work then its the settings your using when you first saved the wmv.
Windows movie maker changes its drivers all the time and that is probably the source of your problem...
Load wmv and drag to sequencer. Click save video button.
Click computer/data button. Use these settings.
preset=custom
file format=avi
resolution=1280x720 hd
framerate=29.97
Click on encoder options
video compressor=mpeg4(native)
video compression setting=4096
sound compressor=mp3 (native)
sound format=48,000Hz,320kbps,Stereo
Click okay, then create button.
Click on avi file and make sure it plays in media player. Otherwise some of above settings will have to be changed.
Now load new avi file into editor then drag to sequencer, save video button, disc,make dvd movie, and burner setting=dvd burner.
advanced button settings...9000bitrates,audio bitrates 320kps
Okay button and create button.
If that doesn't work then its the burner hardware or incompatible dvd player. If it still doesn't work let me know, we can use settings that are for ten year old dvd players. Bye, good luck.