You should be able to log in to *webmail* using the new email address.
This is what will activate it for use. You can subsequently use it
either by webmail, or by adding its details to an email client, such
as Thunderbird, Outlook, etc.
If you've been trying to log into *My Virginmedia*, you should be
using the primary email address, which is the one based on the account
name, and was fixed when you joined VM. The nine other email addresses
you can create yourself are secondary addresses, which can only be
used for email and not for administering the account. Virginmedia
themselves can tell you more about this. There is comprehensive help
information on their website.
Rod.