A global field to global field relationship won't work. gDateEntered seems the wrong field to use as a match field here.
I removed link the dashboard and based on only the months table I am still unable to extract the balances per asset based on the months in a portal. It keeps on giving me the total capital amount and not just up to the date selected.
So when you removed it, what relationships do you have in place now?
Using conventional calculation and/or summary fields to get subtotals of different records requires setting up either a relationship that matches to the specific group of records needed to compute that sub total, use a filtered one row portal with a summary field where the portal filter limits the related records to the group to be totaled or, if using FileMaker 12 or newer, you use an aggregate function inside an ExecuteSQL calculation.