I read it all and it seems that you are asking about Explorer and he is answering about Calibre/Kobo. But there is an easy way to solve this:
OP: Can you see the contents of your Kobo through your computer's file Explorer as if it were a flash drive? (Forget about Calibre for the moment.)
If the answer is "yes", then try fixing your system time.
If the answer is "no", then I concur that you have something more sinister going on.
|