hallo there Sam_nazarko
i have the same problem, how ever i dont get:
Install Error, can’t mount root
i get:
Install failed: can´t mount root
here is what i have tryed:
different psu
different sd card
different raspberry pi
disconnect every usb stick/cable/keyboard
re-download image ( many times)
reinstall osmc onto the sd card(s) (many times)
download the image without the installer and use USB image tool, to install osmc to the sd card
only thing i can think of is that is something wrong with OSMC RC for the Raspberry pi b+ (raspberry pi 1)
you can see my threat here