Hitachi External Drive not seem by mac

Hi there c1defence,

Thanks for joining us in Apple Support Communities. We understand your Mac isn't recognizing your external hard drive when it's connected. We're glad you're here, and we can help.

To start, try repairing the disk with the steps in this link:

Repair a storage device in Disk Utility on Mac

If that doesn't help, have a look at the information here:

If a disk can’t be repaired

We hope this information is helpful. Don’t hesitate to let us know if you have any more questions.

Take care.

Did the drive previously appear on the Mac?

Does the external drive show in a FInder sidebar?

Does the drive show in Disk Utility?

If it shows in those places, it is mounted but the default settings are preventing it from showing on the Desktop.

If it does not show in the FInder then it may be an incompatible format or, if the drive is a model that does not have an independent power supply.

The latter is very common for that low-cost class of drive. Sometimes, reformatting the drive as Mac helps with that; other cases require a powered USB hub to overcome the drive's power demands.