The password for an email account was recently changed, and now when I startup thunderbird it gives me an error for that account. However, I can't go into the Tools->Accounts to try and change the password because it's eating up 50% (1 CPU core) CPU and the hard drive light is on pretty steadily. I've tried starting it up in safe-mode, no good. This is on Windows Vista BTW.
I tried removing the .msf files as per http://superuser.com/a/72091/98705, and then it worked. Still took a while with lots of CPU and Disk access, but it wasn't frozen. And it eventually finished off and it's all working now.