For some reason after running a Windows 8.1 System Restore, Thunderbird no longer worked. It kept producing the following message: "Thunderbird is already running, but not responding. To open a new window, you must close the existing Thunderbird process or restart your system." The problem was that Thunderbird was actually NOT running. Nor did it appear in Task Manager so I could end the Task. Restarting the system did not eliminate the problem. Nevertheless, I decided to save the Thunderbird Profile for the email messages that it contained. I then downloaded and reinstalled Thunderbird and replaced the Profile with a version I had saved several weeks ago. This solved the problem as far as Thunderbird working is concerned. However, I lost all of the pop emails after date of the weeks old profile I had saved. The missing emails were from two pop email accounts. In the Profile that was causing the initial problem and that I saved, the missing emails appear to be present. However, if I copy the Mail folder from that Profile and replace the Mail folder in the Profile that now works, the emails do not appear. Rather, only the names of the two pop email accounts appear with none of the account folders, i.e. no Inbox, Drafts, Sent or Trash folders and their contents. Is it possible to copy certain files/folders from the problem Profile and replace those in the Profile that works in order to recover the "lost" emails. Copying all of the content from the Problem Profile simply causes the same issue with the "Thunderbird is already running" message. I am running Windows 8.1 Pro (64bit). The current version of Thunderbird that is now working is 91.10.0 (64 bit). Assistance to recover the missing emails would be greatly appreciated as some of them are rather important. Thank you in advance for considering my issues.