FYI, I have a panasonic giving me the same "No Disk" error message.
Replaced a bad spindle motor only to have the thing giving me the exact
same message. I was afraid to touch any of the adjustment screws, since
this is probably a point of no return, but since the laser is
emmitting, and won't lock in focus, I suspect something needs
adjusting, or I accidently damaged the laser lens. Still working on it
though.