Razer 13.3 stopped recognising Core

I got a new Razer a couple of weeks ago to replace the 12.5 which is fast becoming a fire hazard
I got it working with my Core, and it was running OK
Then I installed a piece of software which installed Microsoft C++
Now the Razer doesn't see the Core - no monitor, no USB, it still draws power
My old 12.5 still connects OK, so the Core is fine
I've rolled back to a version pre-C++installation
I've also done a reinstall of Windows
Does anybody have any thoughts?
I might just send it back to the shop