Thunderbird/Firefox is already running but is not responding. The old thunderbird/firefox prosess must be closed to open a new window.
I have tried the suggested: In window search type :%Appdata% - see image below as guide Select %Appdata% file folder Select 'Roaming' Select 'Thunderbird' Select 'Profiles' Select the 'profile name' folder look for and delete this file : parent.lock
But when I do access appdata all I find is a Microsoft folder. Properties of the appdata folder are to show hidden files and the number gigabytes in the folder properties are greater that the just the Microsoft folder has suggesting that there are hidden folders. Any suggestions?