Forgot orginal Vendor ID - Can`t access Ebooks

Hi

Is it possible to find ID one used to initially to access ebooks?
Have tried authorizing my computer, but in turn lost access to allready bougth products.
Error code: "This computer needs to be authorized with a vendor ID to open *Title*. To start the authorization process with a vendor ID, click on the continue button."

When I enter Adobe ID, this appears:
"The vendor account you entered is not associated with the item you are trying to open. Try again."