OK - quick update before I go to bed!
I've created a new profile on my PC - I've even changed the USB port I'm connected to and it's new cable as I got another when I swapped the PRS today. Then I did the hard reset on the PRS. I created a new adobe account, I then ran up ADE and authorized with this account - all OK to this point.
I then plugged in the PRS and activated/authenticated that as well all perfect.
I created a new waterstones account with a new email address (the same as the new adobe account as well). I then bought a new book from waterstones all downloaded OK and appears in ADE - I can open it look at it etc on the PC perfectly.
However once copied to either the internal memory or a SD card it reboots constantly again! Well peed off now!
So what's left the PC/installation as a whole I guess?
All I can think of doing now is installing it all on my laptop and trying that? Fortunatly
www.ebooks.com allows you to download multiple times so I'll use that adobe account for testing.
If I get anywhere with this tomorrow I'll let you know. - I know someone else has replied to your post on the ADE forum already with the same problem.
Dave