Question about Outlook Express

I have an issue. I have multiple accounts that I have set-up over the years that I have access to with email addresses that continue to use to this day. I would like to combine all these accounts to a single account and a single sign-on using the alias feature. I ave tried closing each account and adding them to the alias list for the account I like to combine to; however, the system is still saying that the email/account is still in use. Is there anyway I can combine these accounts into a singe account? 

Thanks,