My folders from my TalkTalk account keep disappearing and reappearing.

The folders from my TalkTalk account keep disappearing and reappearing. I have tried lots of fixes suggested by a guy who helps with tech issues but nothing has worked yet. Just before it happened, I clicked to 'compact folders' when prompted. I've done this loads of times before with no issues. I have used Thunderbird for a long time and never had this problem before. The folders seem to disappear when I shut down and restart the computer. Yesterday they came back in about 5 minutes. Today they haven't come back and I've had the computer on for about half an hour. Every time the folders come back, they are Threaded (which I never choose) and Ascending (I always choose Descending). I change them back but next time they revert again. So far, we have: backed up the profiles checked the server settings checked the password checked webmail - working fine refreshed the folders (subscribe) deleted a .msf file Any other ideas? Much appreciated!