G Drive not being recognized on Mac

Hi, I’ve been using my G Drive to back up my mac. Its been awhile since I did it. Now I plug it in and the light comes on on the drive but its not being recognized on the computer. I can’t see it in the disk utility. I did upgrade to the OS X El Capitan, would this effect the readability? I’m not sure how to resolve this and don’t want to loose the contents on the hard drive. Thanks for any help!!

I strongly suspect El Cap is the culprit. Did you backup your system prior to upgrading to El Cp ?

Unfortunately I didn’t back it up before I upgraded.

Do you have access to another MAC with an OS other than El Capitan ?

Can you try another connection cable and a different port on the computer ?

Did you upgrade from one of the OS versions that came with an install disk so you can revert ?

Can yo visit an Apple Store and have one of the guys at Genius Bar take a look ?

Same problem on imac computer on el capitan showed the g drive ok before in finder , and Disk Utility. Now it doesn’t show on either. It powers up and drive seems to be spinning but will not show now. Imac crashed once so may have unmounted incorrectly. Anyhow all normal solutions have failed…ie Changing ports from one firewire to another and to usb and also to another macbook on mountain lion os and no show either. I have no sata ports on either mac to try that port. El Capitan cant be the problem here.
Does anyone know what size the harddrive on a GD4 2000 2T drive I they dont list it now it was refurbished by G tech from a 2009 one in 2012 after previous failure) because one possibility may be the enclosure failing somehow and wondering if the drive itself could be taken out and slotted into a usb/sata dock as here https://www.amazon.co.uk/gp/search?tag=macr0e-21&keywords=usb+sata+dock
So need to know the exact size. No warranty left to use btw so opening it up seems only way.

The capacity is in the name of the device you asked. GD4 2000 2T = 2 TeraByte.

It should work in the dock you mentioned just fine.

OK a small gain. I took the case apart trying to see what kind of harddrive
it had to try the external hd caddy solution in case it was the enclosure
problem only… I fiddled with the connections a bit and then lo and behold
it began to flash and got recognised at last. I managed to download all the
files I needed Hooray! … then I carefully de mounted using Disk Utility.
I left it spinning and powered on. However I then tried turning it right
off and then on again. This time I could see it blinking and trying to
catch but failing to spin. God know what is actually wrong but I suspect
the means to start it in the enclosure is faulty. Dont have a caddy for it
so will take it into some computer shop and see if they can slot the hd
into one. I suspect the hd is ok.