Did the Pandigital just show up in ADE on the old computer?
What software was the old computer running, and what was the tablet running?
Some devices require special driver software to be seen by ADE on the computer.
An example is Sony PRS-350, but true of others too.
Without driver they show up as an external drive, but not as a device in ADE.
There are lots of bugs in ADE2.0. This includes not recognizing certain devices, and not behaving properly if it does recognize them.
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