Player keeps saying no disc why?

There r two reasons that the player says no disc on display. 1)the disc which you insert in your player is really not redable.check out that disc in any other player and confirm whether its working or showing the same fault in other player too. 2)the disc may be perfectly all right, but the lens in the player which reads the disc is either got dusty or the lens is turned faulty. for dussty lens you can clean it with tissue paper and check out .but for the faulty lens its necessary to replace the lens.thats a costly issue.