To cut a long, frustrating story short:
I got to the bottom of this issue of the Helix "not being connected". I tried a mixture of my PC and several laptops. But on my PC I kept getting either no connection or a brief connection that dropped out. After much lost time, I suddenly recalled the instructions about not using a USB hub.
On my PC there were USB connectors on the front of it and several on the back of the PC on the main card.
As soon as I plugged into any USB connector on the back, everything worked perfectly, every time.
So I reckon the USB connectors on the front of the PC were essentially configured as an extension USB "hub".
I just wanted to post this, so that if it saves anyone the frustration and wasted time that I went though (eliminating operating systems and all sorts of other stuff) then great.