I plug the HD into the server via USB, and I can see it under System Profiler>USB but cannot see it in Disk Utility, and it doesn't auto mount to the desktop. My intention is to attach the drive to the server and to share it out so both users can access it. The issue was that only one of the users could access the drive at a time.
#Mac terminal commands mount external harddrive mac
The external hard drive was attached to the Mac workstations and was fully functional - it was working correctly. I have two users who both use Mac workstations. I know you have mentioned that the drive doesn't show in Disk Utility but I'm including this next step regardless: If your drive features both USB and FireWire ports, try both ports (but not at the same time). Attach the drive to a different computer to see if it works and also use different cables and different ports on both computers. Test each component associated with the non-responsive hard drive on a working computer.The same goes for the USB or FireWire cable make sure it's connected firmly at both ends. This includes the power cable, both in the outlet and into the back of the drive. Check all the connections to confirm that they're seated correctly.
Finally, if there is any unusual noise or silence, then it could very easily be the drive itself. If the lights come on and the hard drive spins but doesn't mount on the desktop, then it could be a connection issue.If the power indicator light doesn't come on or you don't hear the drive spinning, it could be a power issue.