First thing wrong is this:
Workbooks(1).Worksheets(1).Cells(20, 10).Values
The property is Value not Values.
Potentially, the second thing wrong is that you are expecting the sum to appear in the first sheet of the first open workbook and it's not there. Likely, that's because the first workbook is PERSONAL.XLSB which is hidden. Unhide it and see if cell J20 holds the value 2.