Problem with Windows. How to fix the bootloader?

Question

Windows

I ran into such a problem, I start the PC, it says the operating system was not found, I found videos on YouTube where people use a bootable USB flash drive.

By pressing F2 many times when I turn it on, I get another white-on-black error: Error 0210 F2 something there (in English, of course)
I keep all the necessary files and codes on the desktop. We need a way to spend a maximum of an hour and not lose data from the desktop and drive D.

In general, I even know why it is. I downloaded a program that will add space to my C drive from drive D. I checked it for virus-total and everything is fine. The program required a reboot. The reboot began, after it this text appeared that the system was not found.
It could also be that I accidentally made another empty drive A system and active.

Answer 1

Error 0210 F2 something there (in English of course)

That's what they would have said right away. This is where everything becomes clear.

Need a way to spend a maximum hour

Let's at least 1 hour 05 minutes.
PS: take the https://sergeistrelec.ru/ WINPE image, go to disk management through winpe, and look at what you did there.