My book essential no access win 7

Hi
I have bought a new 4tb my book external hard drive

I have a 3tb my book essential and wanted to put alll my folders and files on my new drive

So connected both drives to my desktop computer running windows 7 64 bit
I then went to my essentila drive and CUT all the files
Then went to my new drive and pasted then into it
It took all night to do paste in 2.5 tb to my new drive
I switched off and dissconect my new Drive and left in my essentila drive BUT I can see it in device drive and listed all okay also i can see it in drivers and printers
BUT I can not see any thing on my drive or in explorer it is not listed

What have I done wrong please

You should safely eject the drive after when the copy process ends. This may be due to the consequences of an unsafe USB device ejection.

https://support.wdc.com/knowledgebase/answer.aspx?ID=15097

thank you for that but most times i do click the icon on the right hand side and wait for it to say “it is okay to disconnect your hard drive now”

BUT if that was the case you not not give me any information to how I can put it so I can use it again.

hmmmmmmmmm.