The NUC shutdown whilst in use (Windows 10 Pro), it restarted itself, but nothing appeared on either of the display port or hdmi monitors. I disconnected the power, removed the display port monitor, powered on, the light comes on the fan comes on but after about 10 seconds turns off, then it turns back on itself, and repeats. If i remove the hdmi it reboots and stays on, but connecting hdmi or displayport start the rebooting again. I've removed the memory, swapped it out, etc tried different monitors. Always the same, turn it on without monitor it stays on, as soon as you connect hdmi it reboots.
Without monitors connected, is it booting up into Windows and can you access it remotely?
If you can, please download and run the Intel System Support Utility for Windows and save the report to a file. Then, using the paperclip icon below the edit window, upload and attach this file to a response post.
I got a ping response from the machine once for a few seconds, but then it stops, the light stays on. But i've not been able to remote desktop.
This is without monitors connected from boot up, just ethernet and power.
I am not sure what to suggest. If you are still covered by your warranty, you can have Intel replace the base unit.
After verifying that your warranty is still active (here: Determine if Your Product Is Still Under Warranty), you need to directly contact Intel Customer Support to initiate the RMA process (you cannot do this through the forums). Here are pages where you can lookup contact information, including local phone numbers, by geography:
You can use the online forms service or email, but I actually recommend calling them directly. The above links provide local or toll-free numbers in most countries and support most local languages. You could also use the chat service (start here: Intel Customer Support Chat), but understand that this service is offered in English only and is subject to the normal (9:00-5:00 M-F) office hours in the Pacific (UTC-8) time zone.
Hope this helps,