thunderbird can't find my files or folders

After using Thunderbird Portable for nearly a year with few problems, I have just been baffled.

I'd had the flash drive containing T/P in a particular laptop for several days and it was working normally. I removed it briefly and inserted it in another computer without internet access, loaded T/P, looked at a message off-line, then closed Thunderbird, shut off the flash drive, and removed it. When I plugged the drive into the computer in which it had been functioning perfectly an hour earlier, I got a message to the effect that I would have to set up an email account (despite the fact that one had long ago been created); the folders pane was blank. So I went through that exercise. At this point my folders pane had the designated email account with an inbox folder subordinate to it, and a local folders with trash and unsent subordinate to it, only. Eventually I figured out that new imap and local folders had been created; by changing the settings of the addresses for these folders I got my old folder structure back and am able to access the messages.

However, I am not able to download new messages. When I order "download/synch" I get repeated notifications that login information is being sent and that I am connected to the server, but the new messages that I can see on my webmail account are not picked up, nor do I ever see the "checking for new messages" notification.

It may or may not be relevant that when I go to File>subscribe I get a blank "select the folders to subscribe to" pane.

I'd appreciate any help.

Gary Williams