Hi Mark,
To be able to see the whole drive it needs to be converted to GPT
Open an elevated command prompt (right-click Command Prompt, and then click Run as Administrator)
After typing each these commands, hit Enter:
diskpart
list disk
(Make note of the disk number you want to convert and enter it into the next command)
select disk disknumber
clean
convert gpt
Then close Command Prompt
Open Disk Management (accessible by right clicking your Start Button)
Right click the unallocated space on your 4TB drive and choose 'New Simple Volume'
Then if asked, Assign a Drive Letter to the Drive - choose the letter suggested in the Drop Down . . .
Close Disk Management, you should now be able to see the full 4TB Drive in Windows File Explorer!