I have data in a Orders table that I want to use for my calculated field on my Customers table, is it possible to use data from a field on another table?
Are you doing this in an Access 2010 or 2013 WEB database? If not, you should not be having calculated fields in your tables to begin with. That is what queries are for.
Is it a WEB Database (a specific type in Access 2010) or a regular one?
You would normally keep a table of points and it would add a RECORD to the table if an order was over that amount. You shouldn't be updating a field to the value. Adding a record and then pulling their total via a query would be the way it would normally be handled.