Huawei P8 not detected by PC in Fastboot mode

I use
adb reboot bootloader

to get into fastboot mode.

the display shows
"Fasboot & rescue mode

please connect and open Hisuite

LINK

phone locked"

I even installed the Hisuite, but nothing happens and

fastboot devices

returns an empty list.

when the devices is booted up, USB works like a charme - but in fastboot mode windows does not even detect a device?!

any ideas?