HELP: Mail Wants to Start New Account!

Question

Last night, all was well as it has been for over two years. This morning, I opened Mail, and all the folders/files on the left were bigger, and there were icons in front of them. I quit, rebooted my 'Book and restarted my modem (using Verizon DSL).Next time I went into Mail, it wanted to start a new account!
Where is everything, and where did it go?! How do I get it back?

Answer 1

I don’t fully understand what you say. In particular, “there were icons in front of them” doesn’t make sense to me.
What’s the capacity and space available on the startup disk? Take a look at the comments about disk space in the following article, in case they apply to you:
Problems from insufficient RAM and free hard disk space
Even if there is enough space available on the startup disk, under some circumstances (e.g. repeated crashes) Mail may discard the current ~/Library/Preferences/com.apple.mail.plist preferences file and create a new one. This file is where all the account settings are stored. As a result, all your non-.Mac account settings (but not the messages themselves) are lost.
Verify/repair the startup disk (not just permissions), as described here:
The Repair functions of Disk Utility: what’s it all about?
After having fixed all the filesystem issues, if any, and making sure that there’s enough space available on the startup disk (a few GB, plus the space needed to make a backup copy of the Mail folder), quit Mail if it’s running, and make a backup copy of the ~/Library/Mail folder, e.g. by dragging it to the Desktop while holding the Option (Alt) key down, just in case something else goes wrong while trying to solve the problem. This is where all your mail is stored.
You have three options now:
(1) Restore ~/Library/Preferences/com.apple.mail.plist from a backup if you have one. Mail shouldn’t be running while you do this.
(2) Set up your mail accounts again. If given the option to import existing mailboxes or something like that, don’t. Just enter the account information and Mail will automagically rediscover the data in ~/Library/Mail/ when done. You’ll also have to re-configure most of your settings in Mail > Preferences. For spam-related security reasons, the first thing you should do is go to Preferences > Viewing and disable Display remote images in HTML messages if it’s enabled.
(3) Mail may have renamed the old preferences file to com.apple.mail.plist.saved. If that’s the case, you may try trashing the new com.apple.mail.plist and renaming the old com.apple.mail.plist.saved back to com.apple.mail.plist. Again, be sure Mail isn’t running while doing this. Given the circumstances, I would expect com.apple.mail.plist.saved to be corrupt, but apparently that often is not the case and the settings can indeed be restored by just renaming it back to com.apple.mail.plist.
Note: For those not familiarized with the ~/ notation, it refers to the user’s home folder. That is, ~/Library is the Library folder within the user’s home folder, i.e. /Users/username/Library.