Mr bizzy

Hi I'm new to this thing. I have a problem with my 55plate lrd3, the CD player which is a interchanger.when you put a cd in it spits it straight back out with message. Of saying invalid cd what's the problem been told to disconnect battery for twenty mins that didn't work. I'm using the wrong CDs and that I should use only originals but half were originals. So now I've no idea and if I wanted too I can't find a replacement anywhere.