macOs High Sierra External Hard drive problems I have a Toshiba DTC810 external hard drive that was working properly for almost a year. Then, suddenly, yesterday I plugged the drive into the USB port and it wasn't working. I tried to plug him into a Windows PC and everything was fine. 

Does anyone have a clue what could be the problem? My mac version is macOS High Sierra (MacBook Pro 2015) and the external hard drive was properly formatted before use. 

Thank you,
Nemanja
Without more information one can only recommend generic steps.

Since it works on Windows PC, it is not the drive nor the cable.

1- verify if it is the USB plug, by plugin another USB device and see if it works

2- try the second USB plug on your Mac

3- Open Disk Utility in Application>Utility Folder and see if it shows there

If it does not show in Disk Utility, lets hope it i not hardware but it can be fixed by following.

Reset the SMC (System management Controller)

If you've got an iMac, iMac Pro, Mac Pro or Mac mini, follow these steps to reset the SMC:

Shut down the Mac.
Unplug the power cord.
Wait 15 seconds.
Re-attach the power cord.
Wait another 5 seconds, then turn the Mac back on.


But if you've got any kind of Macbook you should follow these steps:

Shut down the MacBook.
Make sure the MacBook is connected to power (ie plug the MagSafe power adapter into a power source and connect it to the Mac).
Press the (left) Shift + Ctrl + Option keys and the power button at the same time, and hold them down for a few seconds. You should see the light on the power adapter change colour or blink to indicate the SMC has been reset.
Release all the keys and the power button.
Press the power button again to turn the MacBook back on.