Unable to access external hard drive

I have a 2TB USB G-Drive that I have been using for the past 1.5 years for Time Machine back-ups and for backing up other data (e.g., photos). However, for the past week I have been unable to access the HD. When I connect the HD to the laptop, I can't see it in the finder, though I can see it in Disk Utility, but I am unable to mount it. I have tried re-setting my SMC, VNRAM, starting the computer in safe mode, but no luck with any of it so far. When I restarted in safe mode and ran disk utility first aid, it did say that there was corruption in the HD and to run first aid while in Recovery, but when I went to Recovery, and ran first aid, it said there was nothing wrong with the drive.

I'm running OS Sierra on a Mid-2014 15" MacBook Pro Retina.

Any suggestions would be much appreciated.