Check the power and data cable
- Check that the power cable is securely connected to the external drive and wall socket (applies only to desktop external hard drives).
- Do not connect the drive through a USB hub, connect it directly to the Mac. Make sure the power adapter is connected directly to a wall outlet, not to an extension cord.
- Ensure the cable is securely connected to both the drive and computer.
- If your external hard drive came with with a Y-cable, use both USB connectors to ensure the drive is getting the appropriate power.
- If you are connecting to a Mac, use the USB ports found on the back of the computer. Avoid using USB ports found on keyboards, monitors or the front of the Mac.
- If the problem still continues, try using a different USB port.
Check the Drive Partition using Disk Utilities
- Click "Go" on the top menu bar, then choose "Utilities" and open the "Disk Utility" application.
- If the drive is not on the desktop or if "Disk Utility" is showing that the drive is formatted in a file system that is not recognized by the Mac OS, the drive can be formatted so the the Mac OS will recognize it.
Check System Profiler
The Mac System Profiler will show you whether the external drive is physically detected by the Mac.
- Click on the "Apple Menu" in the top left corner of your desktop.
- Select "About this Mac" and then click on "More Info" to open the System Profiler Application.
- When the System Profiler opens click on "USB" in the left menu under the Hardware category.
- If the drive is still not visible, try connecting it to a second Mac to verify the issue.
- If the drive fails on the second Mac, create an RMA and return the drive under Warranty.