My Toshiba DVD SD-3980 keeps loading and will not pay DVD's How do I fix it?

When I put in a DVD in my toshiba player it keeps trying to load the disk and the screen on the T.V. will say "Loading", then after say 2-3 minutes of the loading process the DVD player will say "bad disk, or incorrect disk" on the tv screen and display "bad" on the DVD little screen. Any ideas as to what I need to do? Parental lock is not activated. Thanks,
Dafnie

dafnie_walsh@yahoo.com