A short introduction to my problem, and what I've done so far:

1) I've been trying to set up HDR with my PC running to my TV. Both are HDR compatible, I've checked my HDMI cable is HDR capable (successfully connect this to my PS4 Pro and triggers HDR).
2) Initially, I connect the PC and activated HDR on the TV side (HDR is toggled per HDMI port on my TV). At first, the PC displayed on my TV as expected, but with the HDR toggle inside Windows 10 to off. Naturally, I toggled HDR to on...
3) Next, my screen went black and the PC disconnected from the TV input. Now, the only way to achieve a picture again is to turn off HDR on the TV side.

My question - firstly, am I missing something in this process with regards HDR working properly, and secondly, is there a way to untoggle the HDR in Windows without have HDR enabled? The option only becomes visible once HDR is enabled.

Thanks, Jonny