The problem is big and complex.
First of all, I had Windows 10 and installed Fedora on top of it. I have only one hard drive, so I had no choice but to install them on the same drive. During the boot I would simply choose system from boot options. I replaced W10 with W7 and this is where fun started.
After reinstall Fedora was no longer in boot options. I tried to repair this via Fedora netinstall (rescue a Fedora system), but at certain stage (about 6 seconds after start) it just stops and waits until time-out error comes, then time-out scripts activate and console shows up. Same problem with Live CD. I'm not very confident with this interface, so I didn't try to dig in there.
After that I tried to use Boot-Repair. I downloaded Boot-Repair-Disk on USB drive, booted from it and tried different things. When launching recommended repair, it gives me window with this text: Please enable a repository containing the [grub-efi-amd64-signed] packages in the software sources of Fedora release 26 (Twenty (mapper/fedora-root). Then try again.
Some people said that Boot-Repair can't solve the Fedora problem because of it is oriented on Ubuntu, uses apt-get and deb packages, but developer said it can repair Fedora. At least it gave full information about my hard drive and partitions on it. Info is stored here: http://paste.ubuntu.com/25485355/
The question is what is going on? I can't use Live CD, I can't reinstall GRUB2, Boot-Repair doesn't work properly.
Humbly awaiting for help -.-