editing to include additional details.
hi guys. quite excited about sharing this one, I've been battling with this, for the last 14 or so months, not giving up, moaning and complaining, annoying the shit of everyone. which isn't an issue, I have a low reputation as it is, so it honestly didn't really matter. this was also almost 80% as to why I refused to use win10 as my primary device.
let's start with a little background story.
in 2017 June , I bought myself a dell latitude, in case my school wanted my old laptop back. sadly, on windows 10,  my NVIDIA graphics 4200m refused to go on second screen. the second screen option would do nothing at all, and it would not save, or go dark. so that left me with a laptop, that I could not use the evenings at all, due to 100% light perception. and no, reducing brightness, or JAWS screen shade, will not work. those of us with true light vision, will see the light regardless. after posting on here, someone told me to use a Bluetooth keyboard, and close down the laptop lid, which, while it was a neat suggestion, I wasn't willing to settle with it. so after spending about 4 hours on the phone with the Microsoft disability answer desk, they told me that my laptop is not supported on win10, and that I'm missing the entire NVIDIA control panel. I was willing to sell the laptop at this point, when suddenly, I got an NVIDIA graphics driver update. what do I know, second screen works, and I now have an NVIDIA control panel. I can only assume the person who happened to help me understood my issue, and told NVIDIA to allow second screen or something. so that worked beautifully, until I decided to want to replace this dell for, well, quite a number of reasons.
at this point, the game started all over again, from the beginning.  Intel, AMD, nothing at all, would allow second screen. trust me, I literally tried almost all laptops in the shop, 1 by 1, doesn't matter what brand, CPU,GPU, it would just not do it.

so while I have a Lenovo ideaPad, I can literally not use it the evenings. I was willing to duck Tape the thing around, with cardboard, but again, that won't fix college computers the upcoming next year.
in the meantime, I have discovered through sources, that second screen is mainly affected with intel I series 4th gen and above. so if you like, Intel Graphics 4000 still allows second screen, but anything above that will not. I can unfortunately not speak to AMD, as I've not had many AMD devices, nor does anyone who I know of. I can also safely guess that anything above, including NVIDIA graphics 4200m, under win10, will not allow second screen. as far as I'm aware, windows 7 is definitely not, and I don't think 8.1 is affected, either.

I've even, (feel free to laugh) tried connecting my iPhone through Bluetooth, even tried, again, feel free to laugh, using VNC viewer to kill the god damn thing. sadly, I could never find the phone with the laptop, and VNC seemed to be paid on windows, at least the server, which I needed to set up the laptop side of things. the idea was to display the laptop to the phone, then second screen it that way.
so anyways. a few weeks back, I heard the win10 mailing list, over at groups.io, talking about headless dummy ghost adapters, how they allow you to kill the screen. since I had nothing to lose at this point, I went on eBay, and I bought one for £3. I got the adapter today, and it in fact... works!
here's how it works. imagine a tiny version of a USB stick, but with an HDMI port. you then plug that in, and you will hear some device connected chimes. at this point, you will lose audio, but I managed to recover that with NVDA remote, since unplugging the dummy adapter restores audio. then I set my speakers as default device, while the dummy Adapter was plugged in, and audio got restored. at this point, I opened the projection options, clicked on second screen, and  there, the thing is completely, and absolutely, dark. for just £3, (you may have to do some conversion) you get second screen back, if you care for it. I know for a fact that iron cross has also been wanting this for a while, so I wanted to share for those that aren't aware of it either, since I've only seen this being mentioned a few weeks back. it's exact name is headless dummy adapter. they're also known as ghost adapters. it would be interesting to hear feedback from others, whether it works reliably, but from my experimentation, it certainly does.
and if you get any other laptop, just toss the plug into them. much easier than contacting driver manufacturers, or rapping duck tape around the thing, for that matter.
essentially, this little adapter pretends to be a screen, so you achieve the same affect, as if you plugged in an LCD screen, or a TV, through the regular HDMI  cable, which is also why I lost audio at first, since it redirected audio to the none-existing screen. . and for that same reason, it allows you to disable the screen, since it thinks it's a secondary monitor. I'm rather pleased with this, wish someone informed me earlier.