Lg G3 Fastboot mode started.

Hi everybody, i've an issue with my LG G3 D855(Hong Kong). I bought it with the D85510M version (kitkat). I flashed it with the D85510B with "flashtool 1.8, tot file and a dll file" but it stopped at 94%. Since then, i can't access download mode and recovery. The phone stucks in the Logo and after few minutes goes to fastboot mode. I khow that i have to flash the partitions to restore download mode but the problem is that i can execute the command "Fastboot reboot" but not the other commands. fastboot erase "partition" returns: "failde to erase partition". Fastboot flash "partition" file.img returns: "flash write failure". The latest Android ADB drivers are installed (android adb interface in device manager).
adb devices return nothing. fastboot devices : "? Fastboot."
What is the problem ? Help me please... I'm in windows 10 but i have the same probleme when using Ubuntu. please help me...