External HDD won't mount

[noface0711]

I have a relatively new (<2wks) 4Tb Touro external hard drive. Until yesterday it worked without a problem on both my MacBook Air and my desktop PC running Windows 8.1. Yesterday I unplugged it from the desktop and plugged it into the laptop and it didn't mount. Moved it back to the desktop and it didn't mount. Neither Diskutil on Mac nor Device Manager on Windows showed it at all.

I does mount on a friend's Mac, so the drive isn't dead.
It's not a power issue, as the drive is externally powered, so insufficient power from USB can't be the cause. The light on the drive is illuminated and the platter is spinning, but when I plug it into any USB port I get absolutely no response from the computer.

Any ideas?

 

[DelJo63]

Go back to the Mac and export everything to a DVD or CD while you can.
Playing with tools to debug the issue must be done carefully, less it's permanently screwed up.

 

[bluejolls]

I get this often using my MBP and WD 1gb via USB.