I had this problem. There are two major reasons
1. Did you finish the disc? In most DVD burn software there is a finalize
the disk button. After you finalize the DVD you can not modify it. Of course
if it is RW then you can copy it to your PC then edit and erase the Disc and
rerecord it.
2. Old DVD players will not play all kinds of discs. Look in the mannual. I
had to buy a new DVD player for $150 it has a VCR recorder in it too. On top
of the new DVD player it tells what type DVD disc it plays.
Hint, if you want to save money use CD (and burn Video on CD).
Check if you used the proper setting when you burnt the DCD/CD. USA has
different setting than europe and other countries (PAL) . Good luck.