Coby portable dvd player not wanting to play dvds?

My portable dvd player has been cleaned and is still freezing up when trying to play a dvd or will say that it doesnt detect a dvd when I load the dvd in the player, what could this problem be? Dvds are in the correct format to play in the dvd player. This is a Coby TF-DVD7377 7" WIDESCREEN TFT PORTABLE DVD/CD/MP3 PLAYER WITH DIVX PLAYBACK AND USB PORT