How do I get exclusive access to my database

For some reason, today when I want to change the design of a form on my
database, when I click "design view" I get a message telling me I don't have
exclusive access to my database, so I can't make changes to my design (though
I could before).

I tried going to access options, to Advanced, and changing it to "excluse
open mode," but it did not work.

also, I want to be able to open this database from any computer on our
network; I want shared use, so the database can be open anywhere and people
can be entering data freely. which I wonder if we can do now, (but we could).

I want the database to run as it did before, but something has changed. We
did do a "compact and repair," maybe that reset some defaults, or something...