It would not appear in Finder (except during short periods of syncing), unless it is set to Manually manage music or Enable disk use. So, appearing in Finder may not be a good indicator.
Try doing a Reset
while it is connected to the Mac, with iTunes running.
If that does not help, try putting it into Disk Mode
Then, connect it to the Mac and run Disk Utility. Does it appear in the Disk Utility sidebar?