How Can I fix this problem?

I have a toshiba 14" TV/DVD Combi,
Model No VTD 1432, and the dvd player had been fine for a couple of years, but recently when I tune the set to dvd player it states 'Reading' then says 'Incorrect Disc' I have tried several discs but the same message still appears in the DVD screen, even when there is no disc inserted? I have checked the manual but cannot see any answers to this problem? can any one help or say what is wrong.
thanks