For most Sony readers you need a special driver for it to appear in ADE (typical irritating Sony).
To install the Sony driver you must install Sony Reader (free); even if you don't use Sony Reader the driver will get installed.
If you are going to use Overdrive library books with the Sony you will probably hit one of the (many) bugs in ADE2.0.
1.7.2 is the best solution to that problem.
There are lots of bugs in ADE2.0. Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
http://helpx.adobe.com/digital-editions/kb/cant-install-digital-editio ns.html
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172