Excel Formulas not working

Looking for some help on this excel.  Previously VLookup was used and it work but now does not.  I do not understand why.   Here is what I am trying to achieve in the excel attached:

1.  The data in Table 1 is populated by Table 2.  Table 1 is locked when the contractor uses it for us to be able to track data.

2.  When the cumulative total is populated, I would like to be able to pull up a specific month and have the data be accurate as of that month.  

3.  Please Help!