No HDMI Output - PCI blackmagic decklink mini monitor 4k

Hi, I have been using my PCI - blackmagic mini monitor 4K with a 1080P SDI monitor for the last 6 months and its been perfect.

I have just changed my monitor (BENQ SW240) which requires an HDMI v1.4 Input but I can't get it to receive a signal over HDMI?

I have tried:

HDMI V1.4 cables
HDMI V2.0 cables
HDMI V1.4 to Display Port V1.2 adapter

and it doesn't receive any signal.

I have tried connecting it to my Small HDFocus 5 and another HDMI monitor that I have and none of them displays an image.

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Am I doing something wrong, I thought the PCI - Blackmagic decklink mini monitor 4k would work with any HDMI display?

Is this not the case, any help would be appreciated

Thanks,

David