Two possible problems  here.

Firstly, the non-visible application would mean that you wouldn't be able to
see the new workbook  even if you could open  it. (I think.)

Secondly, the active form  has locked excel  (the spreadsheet  engine) while it
is active. To open another spreadsheet, you need to open another instance
of Excel. (I suspect this one is your major problem - I've seen it
elsewhere.)