Do you know what frmat these are in? PAL or NTSC?
Some DVD Players can't cope with movies that aren't in their format, or the TV can't.
It could also be very poor burn quality of the disks. What DVD burner are you using? Are the media +R as again some older players can't handle these, but this can be overcome by setting the book type of the media to DVD-ROM. Further explanation may be needed on this.