I installed Docker on the latest Windows OS and got the following message "Hardware assisted virtualization and data execution protection must be enabled in the BIOS." Hyper V is definitely enabled. However, the Performance tab of the Task Manager tells me that virtualisation is disabled. How do I enable it?
Look into your BIOS settings.
Depending on the hardware, you need a different key or combination of keys to get into BIOS settings at system boot. While there look for virtualization support, and specifically Intel VT-d (I assume here you have an Intel CPU).
Saving and restarting into the OS should enable virtualization.
Edit: This article from RedHat provides perhaps a better explanation of above, see point 4.