A DVD will hold 1 hour of HQ video. If you try to stuff more onto one it 'fits' by degrading the quality. I won't say that is your issue, just something to keep in mind.
As a test, take the same WMV file into Video Copy and Convert.
For output choose Video then Custom. Select H.264 for Compression and 720 X 480 (NTSC) for Resolution. Data Rate should fill in at 8,000 kbps. This will save the file as an mp4 with the same name. (look in Video - My Movies)
Now with our test file, start a new MyDVD project and use that file. You can 'burn' that file to a Folder instead of using a disc, than Play that as a DVD. If it works OK, try a disc.