My MS-Windows 10 crashed during an update and became corrupted. Got stuck in a continuous loop unable to progress beyond "preparing automatic repair". Took me ages to discover a fix. Here are a few remarkable tips!
1. One solution is to repair or reinstall Windows having made repair media on another Win10 machine. But you need to boot from it. You may need to access F2 during Start Up.
2. But if your NUC is connected to a 720p (HD) monitor, oddly, it won't offer you F2 on start up. It doesn't even appear in the boot menu. Adopt a higher resolution monitor and it will appear, but only if directly connected HDMI to HDMI (not via an adapter).
3. Your NUC also won't offer F2 with a wireless keyboard until Windows drivers will boot. So once you have got passed foible (1) and can see the option on screen you can still press F2 frantically with no response. You need to use a wired keyboard to get going again.
Took me four days to discover this, so thought I should share the knowledge.
