Cannot boot Windows 10 after Ubuntu installation

So I was having this idea that I’ll install ubuntu 18.04 alongside my already working win 10.

Keep in mind that I have two older discs (MBR) and legacy bios – main disk 1 TB. On my main disk a made some free space, shrank size making 50GB of free space for Ubuntu instalation. I installed Ubuntu from usb and after that it asked for reboot so I did that. And that’s where first problems appeared.

First, I was not able to boot back to ubuntu at all. After some tinkering I found out on the internet that I should be using EasyBCD as boot manager. Did that, added ubuntu, corresponding partition and I got it. Reboot, boot manager loads fine, win10 working as it used to. But when I tried Ubuntu, I got stuck on black screen with flashing cursor. Was not happy with that. Went for reinstall as someone suggested that something might install wrong. So I deleted the 50GB partition (made free space again) and reinstalled Ubuntu back.

This time really something was running differently. First Ubuntu boot manager welcomed me with all various choices. (Ubuntu, recovery mode, win10 on older disc and win10 on main disc). Tried ubuntu, everything was running flawlessly. But when I tried to boot back to Win10 on my main disc, boot manager appeared with my message that I should repair my pc. And following \NST\nst_linux.mbr is missing or error in it. From this point I cannot really move further. Ubuntu is still running fine. I’m able to run Win10 on older disc but when I try to boot using main one it ends on this message.

I’ll be very greatful if anyone provides any idea how to fix my problem without scraping main storage.

I had an idea if there is some interference with ubuntu boot manager and EasyBCD that is surely still working on the storage. Also I went through the directories via ubuntu bash and at this point I did not lose anything from the main storage.