I need VBA code to make each combobox option on a userform open an excel workbook ...

Inactive and unresponsive mean two completely different things. Do you mean that the file opens but does not have focus? Or do you mean that the file opens but does not respond to any user input?

I have not tested this but this form of the command may solve it:

Formula:

 Workbooks.Open(Filename:="Workbook A").Activate

If you continue to have problems I will try to set up a test.