Sounds like your computer is not recognizing the Sony PRS-650. Are you using a Windows PC or a Mac? No software will work if your computer doesn't know the 650 is plugged in.

Try using a different USB port on your computer and see if it recognizes the 650. If not you might need to uninstall the iRiver driver, restart the computer, then plug the 650 into it. Sometimes similar drivers interfere with other connections, and the iRiver driver might being doing that.

When a Windows computer recognizes the 650 you will see something like READER (X: ) in Windows File Explorer. I'm not sure about Macs. Once you get the computer to recognize it then you can use the Sony Reader Library software or calibre or simply drag and drop books to the 650.