Headers

I have a document that has already been formatted with headers in 3 sections.
I have changed the set out slightly and added another section at the end
which changed fine but I am unable to add a new section in the middle of the
document.
I have looked at all the things in the help tool.
I have tried page breaks and adding new pages but they just stay the same as
the section before.
I have tried to unlink it from the previous page as help tells you to but it
doesnt work.
Please help me!