My iMac won't re-find my USB mixer.

The iMac has been running audio through the mixer fine using the CODEC for months, which it installed automatically when I first plugged the mixer in.
But now it's been lost, I can't seem to be able to re-install the CODEC at all. I've tried restarting the iMac, the mixer, changing the USB port, everything that I can with my limited knowledge of Macs anyway. I've also used the Disk Utility facility with no results and trawled through /Library>Audio /Library>Extensions etc etc.
Any help on how to get the iMac to find the mixer again and install the CODEC would be great.
Cheers! James.

swap out the USB cable
try the mixer with a different computer. Maybe the mixer is the problem. take a look in Apple Menu > About this mac > More Info... > system report > USB and see if the mixer shows up there.
Maybe there is a driver or other software on the mixer manufacturer's site that would help, or a forum.
take a look at Applications > Utilities > Audio Midi Setup; see if the mixer shows up in the left column, and make sure it's not muted.
take a look at system preferences > Sound > input. Maybe you need to select it as an input.
the driver or whatnot may be in ~/Library rather than /Library. ~/Library is hidden by default; to see it, go to the Go menu in the Finder and hold down the option key.

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