1) If you already have an up to date Adobe account with associated email, you need to register it with ADE.
menu/Help/Authorize Computer (Library/Authorize Computer on the older more reliable v1.7.2).
2) If you already have an Adobe account/ID and have books that have been bought using it, then you should change the email associated with that account.
Login at the adobe.com website ('sign in' near top right), using the old email the account is currently associated with.
(Doesn't matter if this is no longer valid as an email address, it is still valid to access your Adobe account)
Choose 'My Information' on the 'Welcome' dropdown, enter your new email in the appropriate place, and confirm changes.
You will later need to validate that new email address by clicking on the confirmation email it will send.
Then follow step 1.
If you have an old account and the email is no longer valid and you've forgotten the password, try Adobe Live Chat to get access to the account again.
3) You need to create yourself a brand new account.
Click the 'sign in' and choose 'Dont' have an Adobe ID'.
Once you have established oe, go to step 1