If you haven't checked the Devices sub-forum of the Calibre forum, you might want to read this
....if you have read this already and it is of no help, I would post in that sub-forum. I have not experienced this problem, but it has been mentioned before and seems to always be associated with a corrupted book file. (it appears a singular corrupted book file can cause the PW not to show ANY books). Good Luck....if you find the answer, please post it for everyone.