MY EXTERNAL MICROPHONE IS HOOKED UP TO MY BERRINGER MIXER AND I AM USING AN HP COMPUTER WINDOWS 7 VISTA.
I HAVE BAND IN A BOX 2019 AND ALSO HAVE THE REAL BAND.
I WOULD GREATLY APPRECIATE RECEIVING ANY ASSISTANCE ON THIS ISSUE.

Welcome to the forums.

Hopefully, this Video might get you going:

That link VideoTrack provided is definitely useful

To further expand on that, in Band-in-a-Box go to Options > MIDI/Audio Driver Setup and select the Audio Setting button on the bottom right.

What Audio Diver are you using? By default, it should use WAS. If you are using an Audio Interface, you will probably want to select ASIO and set your preferences in the ASIO control preferences by selecting 'Audio Drivers...' - the options under input drivers should align with your Behringer interface.