Default [Q] Fastboot - Black Screen

Hey,

iam not a native speaker so excuse my gramma and some bad words.

I got the following problem:

I've already rooted my Kinde Fire 2 and got installed TWRP and Cyanogenmod. Now i want sell my Kinde Fire 2 and need to get the original Rom wird the original Bootlader. Everything is fine with adb, the Devices is listed but when iam trying to boot in the Fastboot Mode i get only a black screen and nothing is happening, even the LED is not lightning.

When i start the Kindle Fire with the button, its booting normaly. Whats my mistake? Bad Factory Cable or is something wrong?

Thanks for help.