Vincent, the trouble may be that your drive is formatted in such a way that your Mac can't read it (or you don't have the utility on the Mac to read it - some drives like NTFS may require extra software to enable that function).
While it's possible to move it between PC and Mac, you can't just grab the database from the other OS, it either has to go to an external drive first, or be exported as a backup / restored.
Given that you have another computer with Windows, that's your best bet rather than trying to kludge it into the Mac and going through the path change headaches; the best thing to do would be to first install rekordbox on that machine, then migrate your files and folders into the same locations. If the username on the new computer is different than the old, that will create an extra step, but let's start here and give me whatever info you can so I can give you the proper instructions.