Can't get authorised

I have a Sony PRS350 which has been talking to Sony Reader for PC happily for years, i.e. AdobeID is set up and working. I have now had to purchase a new computer and, obviously, want this to support my eReader. However, when I try to authorise my computer with the Adobe ID details I use on the other setup, I get an error which is "Unable to authorise this reader. Contact Sony support"

I want to understand why this is happening.

Second, I want to know if I can get round it. Because it's a new PC, it's never been linked to the eReader, and the PC does not have an ADobeID. If I create a new AdobeID (does the eReader have to be connected at the time I'm doing this?) will this 'lock' all the books that I've previously put on my reader (obviously using the existing AdobeID).

Thirdly,I've got a lot of books I've purchased, as opposed to borrowing from the local library. Am I going to be able to put these in the new Sony Reader for PC app (and read them) or are they permanently tainted with the old AdobeID?

I was a computer programmer for 27 years. Why is this so hard?