I had this same problem and couldnt figure it out. Several dvds were fine with clear audio and video. Then, all of a sudden all I got was video - - - no audio.
It took me a long time with a lot of trial and error, installs and uninstalls, but I finally figured it out.
1 - first of all, windows dvd maker (WDM from now on) does not support mp4. I tried installing additional codecs to support mp4 and probably messed things up more by doing this. Stick with avi and you will be okay. If your files are in mp4 format, it's easier to convert to avi using another program, then burn the avi with WDM.
2 - Open WDM, load an avi file, then click "options". Click "compatibility". If there is a list of codec programs listed, uncheck all except for "AVI decompressor".
Once I did that, DVDs burned fine once again with clear audio and video.
Summary - - - avi files only - - - no other codecs selected except for avi decompressor.
It worked for me - - - hope it works for you too.