Windows 8.1 x64 is not recognising my Sony PRS-650 in Digital Editions 3.0. The Adobe ID is the name on both computers and is authorised in the Digital Editions menu. When connecting to the new machine Digital Editions does not display the device in the left hand pane when it is connected. Version on old machine is Digital Editions 2.0.
Just resolved this by installing the Sony EReader application, probably installed some drivers as well as the app.