Your laser diode on the reader head is either dirty or no longer operational, try cleaning the laser diode, if accesable, very gently with an ear bud in a circular pattern, if that doesnt sort the problem it will have to be repaired by a technitian.
Have you tried holding in the timer button in for several seconds..? Some systems require pushing 2 buttons at the same time.. to disable timer.. and switching to manual reset..!
Probably what is happening is that the lens is dirty so can't read the disc. Cleaning it might restore the operation, but if the lens is damaged it will not.