Mac pro 5,1 no longer recognize 27" cinema display microphone

Have you done a PRAM reset, CMD+Option+p+r...

Reset NVRAM or PRAM on your Mac - Apple Support

In fact, do 3 in a row, takes a bit of time.

1.. Shut the machine down.

2.. UNPLUG the power lead to the computer and any peripheral devices.

3.. leave it for 10 minutes.

4.. Hold power Button in for 10 seconds

5.. Connect everything back up and restart. 

Fingers crossed, but not all that hopeful.