DeDRM plugin

Hi. I'm coming crazy because I cannot install in calibre the DeDRM plugin, even if I did all I read necessary to do. I hope to receive some help.
This is what I've done:
1) I downloaded DeDRM_tools 6.5.1; I extracted from the archive the DeDRM_calibre_plugin and I installed that plugin in calibre.
2) I installed the KindleForPC, and using it I got my book, contained in an azw3 file.
3) I read some ReadMe (I can't remember where) and I learned that in order to have the plugin working the PC mist have Phyton 2.7 and pycrypto installled as well (I downloaded pycrypto 2.6). I did that. After the installation was done, I deleted the book form the calibre archive and I re-imported the azw3 file.
4) loooking in calibre 'preferences' I saw that DeDRM must be configured inserting the proper key relative to your amazon account. I got the key and inserted it.
Despite to all my work, the DeDRM plugin doesn't work and if ask calibre to convert the azw3 file in another format, e.g. a epub format, caliibre tells me the file is DRM proected so a conversion is impossible.
I thought I did anything that was needed for the DeDRM plugin working.
What am I missing?