can't read old emails (Tbird portable not finding my profile)

I can think of a couple possibilities. The first is that Thunderbird was being launched two different ways. Running ThunderbirdPortable.exe directly or via the platform will use the profile within ThunderbirdPortable\Data\profile. Running thunderbird.exe directly will use a local profile. If you pin Thunderbird Portable to the taskbar using the Windows taskbar pinning, it pins thunderbird.exe in local mode with a local profile. If you were accidentally running it one way vs the other, this could be why your profile isn't showing.

The other possibility is that your prefs.js file within ThunderbirdPortable\Data\profile got corrupted. This will cause your mail accounts to disappear. Restoring an earlier copy from a backup will fix the issue. If you don't have a backup in the form of prefs-1.js, etc within ThunderbirdPortable\Data\profile. You could try substituting one of those in, after making a full backup of your profile to be safe. If that fails, you'll need to recreate your prefs.js file: http://kb.mozillazine.org/Recovering_a_profile_that_suddenly_disappeared...