You can probably transfer files by 'sideloading'.
- Make sure the reader program on the Nook is registered with the same Adobe ID as you ADE on the PC.
- If you can't get that to work, try downloading the Bluefire app to the Nook and registering that with your Adobe ID.
- Use ADE to download the files and arrange the DRM aspects (getting the .acsm file initally then downloading the appropriate DRM .epub file).
- Use a file manager (such as Windows explorer) to copy the .epb files from the PC to the Nook.
- You should then be able to read them on the Nook using the reader program or Bluefire as in steps 1/2.
If the books are not DRM, no need to use ADE (though you can if you like). Just get the books by whatever means onto the PC and copy them to the Nook.
You may find Calibre and excellent program to help download/manage/transfer to Nook non-DRM books .
If the books are library books, you can install the Overdrive app on the Nook. That app will let you borrow, download and read library books directly on the Nook without needing a PC/Mac at all.