Mac Mini doesn't read DVD's

When I insert any DVD into my Mac Mini it says Disc not able to be read by this computer.
It reads CDs fine.. I tried to start the DVD player app and it gives an initialization error and that a valid DVD player could not be found..
It does have a DVD drive:PiOnEeR DvD-Rw DvR-K06
Any idea why it would read CDs not DVDs and appear to have lost all DVD functionality??

Any help would be greatly appreciated