This can be caused by various reasons.
What brand/model is your DVD-player?
What media did you use? And what speed?
Some DVD-players are picky with media, others do not play "wrong" discs (eg. some players are DVD-R only and will not play DVD+R even if they can).
Do you have any other media avalible? If your burned on a DVD-R for instance you could try burning it to a DVD+R and try again. Report back with your findings