Just for information:
To be able of boot a just installed system in a ms-dos partition table with a /boot separate partition, I had to mark it with the boot flag.
If you don't do it so and the system boot is impossible, it will be the necessary boot the system using the live CD/USB, then launch KdePartitionManager with "root" password, select the /boot partition and in properties of the context menu check in Boot flag, click in apply to confirm and reboot.
Maybe it's a very elemental task, but I did know it.
Please, sorry if it was already written in some tutorial.
Regards.