My Laptop not recognizing 2nd WD HD?

My laptop is recognizing my “My Book” 1.5TB, but is not recognizing the 3TB My Book. I did some research and some are saying you have to change the status from offline to online, but when i go to my computer, i don’t even see the second drive on there. One drive says CD Rom F:, i thought that was the 2nd HD. Can some one please help, i want to transfer all my files from my 1.5 TB to my 3TB. Thanks in advance.

If you connect only one drive are you able to see it?  Now with both drives connected, what do you see in device management?

the drive shows when just one is plugged in, when I plug the second one in, the drive never shows in my computer?

What OS are you using? You have to go into Disk Management to see the drive scroll down where it shows the drives in bars. What color is it and what does it say? Does it have a drive letter assigned?