DVD Recorder/Player..Not Reading Dvd's,Takes 1-2...

Question

I Have A Couple Of Used Dvd Reorder/Players That Load The DVD, Than Attempt At Reading The Dvd, A Long Atrtempt To Read Ensues, Then Units Either Tell You By Ejecting The Dvd,Or Stopping The Attempted Reading. I Actually Have SOME Dvd's That These Players Will Read,But Probably Only 1, Or 2 Out Of Every 15 Dvd's.