It isn't completely obvious what has happened, but my guess is that
a. you used to use Word 2000 or Word 97
b. your data documents were in Word format (in a table in a Word document)
c. you have moved to Word 2002 or 2003
d. when you create a new mail merge main document and try to connect to the
data source, you can't find/recognise the data source you created before.
When you entered your data for your first mail merge document, do you
remember saving it? In Word 2002/2003 it is saved in Microsoft Access ".mdb"
format: to save it in any other format, you have to work a bit harder. You
don't have to have Access to use these .mdb files.
Once you have saved your data source, you can re-use it by checking the "Use
an existing list" option in step 3 of the Mail Merge Wizard, then finding
the .mdb you saved. If file extensions such s ".mdb" qaren't displayed on
your system, look for an "Access" icon (it has a key on it) next to the
file name instead of the Word ("W") icon you are probably used to seeing.
If that isn't the problem, please can you tell us
a. which version of Word you are using
b. what you are actually trying to do
c. what has changed since it used to work.
Peter Jamieson