My DVD player stopped playing dvds but it reads Mp3 and cd's.. why?

This is common in dvd/vcr combos and thin streamline dvd players, internal heat is one factor and bad processor chips, try unpluging the unit from the wall and let it sit for 24 hours (so internal voltage drains totally) then plug unit back in and try loading a dvd, if it fails to read it,come back and tell me(us) the model number and brand and I'll help you further.