the clues are here
I have upgraded my PC and
Wrong key
DeDRM v6.5.2: Failed to decrypt with key default_key after 0.1 seconds
DeDRM v6.5.2: Looking for new default Adobe Digital Editions Keys
Seems you have changed/ lost/ uninstalled the free ADE key. [ your ADOBE ID ]. you can get that back my logging into adobe web site, if you can remember the email that you would have used before
you are looking for an Adobe ID which would have been written into the registry of your PC. That survives most things , though, so it is strange that you don't have it.I did not lose mine when I upgraded from windows 7 to 10 .
A fresh install of Windows would have wiped it. it is possible you have more than one ADE ID and you need to install the one that matches those books. AFAIK, a PC can only store one such key.
try here & use the forgot password option. ( but you have to know what email account you used to use )
https://helpx.adobe.com/nz/x-product...nt-change.html