Cybook Muse Light does'nt recognise main memory

[jean5]

Hello.
I recently encountered this problem:
when I use my cybook muse light, books that are in the device main memory don't appear. collections I had made have also disappeared and attempting to create new ones fails.
Books on a SD card still appear and can be read.
removing and putting back the books hasn't worked.
the use of CHKDSK on the main memory didn't find any error or defective sector.

edit:
Another problem that I discovered later is that when I finish at least some of my books on the Cybook, the go into the new category, rather than the already read one.
After a while, I discovered that in fact, the categories simply don't change anymore, reading something don't put it in the currently reading category... new edit: in fact, a few books can change categories normally, but only a few. Some book also don't show their cover. I think the books behaving normally are a subset of the one with covers, but maybe I just haven't found the exception.



Thanks to any help in finding what is going on and how to solve it.
Sorry for any mistakes in spelling, English is not my first language.