It could be the drive is belt-driven and that the belt is worn or stretched or fallen off altogether. This is a common problem with some of the drives C= used. I think the Epson SMD 400 was good for this problem. The Chinon drives are generally more robust, imho. Take a look at what kind of drive you have and then trouble shoot from there. It is also possible the the case has bent or shifted so the button doesn't clear the hole in the case, causing the disk not to go all the way in. Take the top cover off the A500 and try booting it again with the button free (this kind of problem I've had happen to A600/A1200s and probably the a500 could do it too).
