I tried to use some DVD－R/RW discs AVN4430 system, but they wouldn't play back. Could you explain why?

When using a DVD-R/+R/RW disc, note that only discs recorded in the video mode can be played. Discs recorded in the VR mode and audio mode cannot playback. Please also note that the Region Code of the DVD must match that of your country's or be "Region Free! for the disc to play back on the system. If not matched, playback is not possible.