So I've had an Intel NUC (DC3217IYE) for around 3 years and it has run, as far as I can remember, without any issue what so ever. I purchased it pre-built from Playtech with Windows 7 installed and an extra 4GB of RAM. It has a 40GB SSD (can't remember if this is standard or an added extra?).
It's plugged into my lounge TV and is generally on 24/7 (obviously in Sleep when not in use).

As soon as some of these early model Intel NUCs were out, people complained of overheating issues, but I've never experienced anything of the sort.

Recently I upgraded to Windows 10. The update process went fine and things were normal. Then a week or so after the upgrade I woke the NUC out of Sleep and noticed it was stuck trying to boot within the Intel Boot Agent but couldn't find anything to boot to. I hadn't really seen this before so just powered off the NUC and turned it back on. It went back to Windows fine.

A couple of weeks later I experience the same issue and now it almost always gets stuck in the Intel Boot Agent. After doing some Googling and as far as I can see this behaviour goes hand in hand with overheating. I can get to the BIOS and have seen the temperature well over 70C, however even when I start the NUC from cold, it's still going to the Boot Agent and not getting past it. Does this mean the SSD is stuffed? The BIOS still lists the SSD as the bootable device, however it can't find it when trying to boot.

Anyone experienced anything like this? Or could help me better diagnose the problem? Are there any other things I could be trying?