It may be possible to properly secure a database on the first try, using
only Help and the Wizard, but I don't think I have encountered anyone who
has actually done so.

Access User and Group Level Security is not a trivial matter -- it is rather
complex. You should visit
http://support.microsoft.com/default.aspx?scid=kb;en-us;207793 and download
the Security FAQ paper. The last time I downloaded a copy and read it, it
was 39 pages, and there is no "filler" material. Read, re-read, try, come
back and ask specific questions.

There are a number of steps -- if you miss one, you may (as you have seen)
leave your database so insecure that most anyone can get it, or you may make
it so secure that even you can't get in.

Thus, don't try securing the only copy of your database -- be sure you work
on a copy of it, and keep a clean, unsecured copy safe (probably beneficial
to keep it offline, so you don't do something to that copy accidentally,
too).

 Larry Linson
 Microsoft Access MVP