re; I was trying to switch default email accounts, Hughes.net was the default and Yahoo the secondary and I wanted to swap these around

How to set the deafult account: Tools > Account Settings or right click on mail account in Folder pane and select 'Settings'

The default account will be displayed at the top of the list. Select the account name you want as default click on 'Other Actions' select 'Set as default' click on OK

I'm perplexed as to how you managed to alter anything to do with address books by doing the above.

There are two default address books in Thunderbird. Both of these address books can be copy pasted between mail accounts.

Personal Address Book is called abook.mab Collected Addresses is called history.mab

These are stored in your Profile folder in the mail account name. But it would need your old mail account to be intact in order to copy anything from it to another mail account.

• http://kb.mozillazine.org/Profile_folder_-_Thunderbird
• C:\Users\Windows user name\AppData\Roaming\Thunderbird\Profiles\Profile name\ mail account name

The AppData folder is folder is a hidden folder; to show hidden folders, open a Windows Explorer window and choose "Organize → Folder and Search Options → Folder Options → View (tab) → Show hidden files and folders".

If your original mail account is still there: Profiles\Mail\mail account name You could simply recover it. Info here:

• http://kb.mozillazine.org/Recovering_deleted_mail_accounts

Remember, when performing any changes in Profiles folder, Thunderbird must be closed first.