Windows 10 OEM License & Dual Booting UEFI

[Going Bald]

Hello everyone, thanks again for all the help in this forum, got me to have Sierra working great, and Yosemite before!

As I just moved to Sierra, i now have to use Clover and dual booting doesn't exactly work as it used to, and I am wondering if I will lose my OEM license by totally formating my Windows 10 drive (including OEM partition).

To begin with, I use 2 SSDs (One for Windows 10 and one for Sierra) + 1 HDD to stock data.

Here are the steps I followed :

1) I installed Sierra with all hard drives connected (maybe a mistake?), and totally formatted my ex Yosemite drive to install it, everything worked properly following the guide, everything fine here!

2) I installed Windows 10 on my second SSD (had windows 7 before), by making a usb drive with media creation tool from microsoft website. For this installation, i unpluged every other hard drives as I thought it could mess with clover if I didn't. Windows 10 works great, I activate my OEM license for the first time and good to go.

3) I plug again everything, boot on clover, Sierra rocks, I try launching windows 10, quick loading wheel and... black screen. I change boot order, now windows 10 boots when i launch it from clover, and when I launch Sierra the Nvidia drivers are turned off, i activate the drivers again again, reboot so it activates, come back, still unactivated. Seems there is a problem here, and booting from clover still show many legacy partitions (for windows), one EFI Windows and EFI Sierra that seems to work properly depending boot order but couldn't find any order that works for all.

Searching the forum I found this page and realized I maybe should have used Rufus to prevent installing Windows 10 in Legacy mode. I am not sure I really got the differences and what UEFI and Legacy are and how it works (any way I could know if win10 is installed in Legacy or UEFI mode?), but I am thinking formatting my whole windows 10 drive to install it again so that it might solve the problem, what do you think?

More importantly, if I format all my Windows 10 SSD's partitions (including the OEM one), will my OEM license be still valid?

Thank you all for your help, here is my detailed setup in case it helps :
- Bitfenix Prodigy Black
- Gigabyte GA-H97N-Wifi
- I7-4790K (4.O Ghz)
- EVGA GeForce GTX 970 Superclocked ACX 2.0
- Crucial Ballistix Tactical 16Go
- CS550M Power supply
- Seagate Barracuda 1TO
- 2x Samsung SSD 850 EVO 250 Go (one for windows and one for MacOs).

If you have an icon at the Clover screen labeled Boot EFI Windows from EFI then you have not installed Windows Legacy Mode.
Another check is to launch the Windows disk management tool and look at your drive structure. If you have a WinRe Tools partition, Microsoft Reserved and EFI partition in front of your OS partition then you are installed UEFI mode.

See https://www.tonymacx86.com/threads/guide-multibooting-uefi-on-separate-drives.198869/

When you registered your OEM license key your hardware (board and CPU) serial numbers were recorded with your license key at Microsoft. Re-installing is OK to do without losing the key.

 

[vulgo]

I plug again everything, boot on clover, Sierra rocks, I try launching windows 10, quick loading wheel and... black screen. I change boot order, now windows 10 boots when i launch it from clover

Is it possible you have installed Clover on both drives?

 

[vulgo]

Is there a way for me to check it?

I don't know. You said you changed the boot order but mentioned Clover starting both times, in at least one configuration apparently without NVRAM.

 

[Going Bald]

Is it possible I installed Clover on my other SSD at post-installation with Multibeast? I have no idea how I could have installed it on the second hard drive another way.

By default Clover installs on the drive on which you booted an OS. What you may have done is to install it both Legacy and UEFI. Check your EFI partition on the Mac OS drive - is EFI/Clover present?
Check the root directory of the Mac OS drive - is it there also?