The dvd is not loading and will not play. the cds are working fine.
how long have you been using this player? I suspect the laser (lens) of the player. I think the laser (lens) is weak that's why it cannot read data/files on DVD discs.
To confirm if actually its a laser problem, insert an Audio CD into the player and see if will play. If it plays, then obviously, your laser (lens) is weak. But if it doesn't play Audio CD, then it might still be the laser (lens) or a mechanism problem.
Get a lens cleaner, use it to clean the lens. If that doesn't solve the problem, get a screw driver, open the player's cover so that you can gain access to the lens, use a cotton board to clean the surface of the lens. This should clean dust or dirt that might be on the lens.
If non of the above solves the problem, then know that you need to replace the laser to a brand new one.
To replace the lens, remove the bad laser, use it as a sample to get exactly the same type and do the replacement. Note that replacing a laser (lens) needs a professional touch, so if you cannot replace the laser, get it to a repairman to fix it for you.
Once this us done, your player will play all DVD discs again.