Roy W

My MZ-DN430 has decided to display "no disc " when I try to play it. The display seems OK and it shows menu, also battery condition and shows that disc is turning, and I can hear motor running until the "no disc" is displayed. Can someone help ? I wonder if it simply needs to be reset to original settings, or if there is something else I could look for, perhaps a "disc in" sensor or dirty lens( or pick up ). I have experience as an audio technician ; have been retired a few years, spent a lot of time working on cassette walkmans etc. but no experience servicing minidisc machines. Hope someone knows the answer even if it is that the unit is toast ! Thanks, Roy W