Thank you for your very quick response.
1. I believe most of the ebooks were purchased from a different account (which was an original email address) however under 'Help' and 'Authorise Computer' both the old account and my new email address (account) are shown. Non of the ebooks are free.
2. There are only 2 books displayed which I purchased in November this year which are 'active'. Non of the remaining ebooks can be viewed within ADE.
3. I did as suggested and de-aurtherised my computer and the reauthorised it.
However I still have the same problem!
I dont know if there's anything else wrong with my ADE account as I have purchased a number of ebooks during November and December via the Sony site (I have a Sony eReader - PRS-T1) but non of these are shown in ADE.
Still open to any advice/suggestions.
David A Jones.