Can not start Windows 10 after installing Ubuntu

I had so this idea to install ubuntu 18.04 at the same time as my already winning winner 10.

Do not forget that I have two older disks (MBR) and the legacy bios – 1 TB main disk. On my main disk, a free space, a small size have been released, leaving 50 GB free space for installing Ubuntu. I installed Ubuntu from USB and after that he asked for a reboot, so I did it. And this is where the first problems appeared.

First of all, I have not been able to restart at Ubuntu at all. After some manipulations, I discovered on the Internet that I should use EasyBCD as boot manager. Ubuntu added, the corresponding score and I got it. Restart, the boot manager loads very well, Win10 works as before. But when I tried Ubuntu, I was stuck on a black screen with a blinking cursor.
I was not happy with that. I went for a reinstallation because someone suggested that something could go wrong. I've therefore removed the 50GB partition (freed from space) and reinstalled Ubuntu.

This time, something was really different. The first Ubuntu startup manager has hosted with every possible choice. (Ubuntu, recovery mode, win10 on an older drive and win10 on the main drive).
Tried Ubuntu, everything worked perfectly. But when I tried to restart Win10 on my main disk, the boot manager appeared with the message that I needed to repair my computer. And after NST nst_linux.mbr is missing or error.
From this point I can not really go further. Ubuntu still works well. I am able to run Win10 on an older disk, but when I try to boot with the main disk, it ends on that message.

I will be very grateful to anyone for giving us an idea of ​​how to solve my problem without removing the main storage.

I had some idea of ​​the interference with the ubuntu startup manager and EasyBCD which surely still works on storage. In addition, I have browsed the directories via Ubuntu Bash and at this point I have not lost any of the main memory.