If you plug the new Promethean screens into your laptop's HDMI port and nothing shows on the Promethean screen the steps below will likely resolve it.
This generally seems to be an issue when not plugging directly into the Promethean screen ie plugging your laptop in to a HDMI cable that then goes to a port on the wall/bench, before additional cabling takes the signal up to the Promethean screen. This issue also seems to be mainly affecting the newer laptops; older laptops seem to be generally fine with this.
So here's the steps:
Plug the Promethean screen into your laptop via the HDMI port using the longer connection (so not directly into the screen)
On the laptop, right click on the desktop and select 'Display Settings'
In the new Window, scroll down the right hand side and select 'Advanced Display Settings'
Change the top drop-down to 'Display 2: APLX-65'
Then at the bottom of this window change the Refresh Rate drop-down box to 29.970Hz or another rate as 29.970Hz didn't work last week but 25Hz did
What you see on the laptop should then appear on the Promethean screen all being well
Other things to check are the resolution - laptop should be 1920x1080 and Promethean screen the same with the active resolution as 3840x2160
Alternatively use a VGA connection with the screen and laptop as this seems to work straight off
