Referencing a cell in another worksheet within the same workbook
 

I have a workbook with contact names, numbers, and a combination of both. I
have a landscape version and a portrait version. I want to only update one
and the other automatically updates. I used the "=" sign. When I first
created the workbook, everything worked fine. I've since made some changes by
deleting and adding. Now some cells don't work. I've tried using the "="
sign again, changing the format to General and Number, but some cells refuse
to work.
Please help....
Thanks so much.