Hi there,
I also have a 650 Reader and found a really handy guide on line that takes you through everything step by step. To read a book with digital rights management you basically need to get an Adobe ID (if you don't already have one) and authorise your computer and your Reader. This is covered in the guide I found though. It's on Sony's support website. Follow this link:
http://support.sony-europe.com/contacts/email/email.aspx?site=odw_en_GB
If you type prs650 into the search box there's a 'getting started guide' that comes up in the list - the bit about getting the Adobe ID you need is in section 5.
Hope this helps - it worked for me!
