Question about Outlook Express

I cleaned up my computer and accidentally moved my "Outlook Files" folder.  My email stopped working and I received the message:  Task '*** Email address is removed for privacy *** – Sending' reported error (0x8004010F): 'Outlook data file cannot be accessed' (and a similar one for receiving).

After a great deal of fussing with the program I finally realized what had happened and moved the folder back where it belongs.  Meanwhile I had created a new profile, but have now set it back to the original profile.  It still doesn't work (ie, won't send or receive emails; I still get the same error message). 

I have another data file directly in my Documents folder which the program also accesses.  That stuff is showing up okay.  I would really like the program to just work off that one data file, but haven't been able to figure out how to make it do that.

If I go into my "Outlook" profile (the original one), it lists three data files:  two of them are identical, the one in my Documents folder.  The other one is My Outlook Data File(1).pst in the Outlook Files folder.   I set one of the ones in the Documents folder to the default (the other one won't allow me to do so) and it still acts the same.

The problem is that I really don't have a clue what I am doing.  We have profiles, data files, defaults, accounts and all this stuff that I don’t know how it all fits together.  Does it all have to be so confusing?  Can someone explain in simple terms how this works so that it can make sense to my simple mind?