my k4b was unbricked wrong kernel

Hi there, Yesterday I unbrick my k4 follow the guide of geekmaster but at last when I did all steps, my kindle can't enter the main screen. I found my mistake that i used the kernel ver.5.0 instead of 4.0 (wow! I don't know how can I do this mistake). Up to now, I can't even enter fastboot mode because my PC can't recognize my kindle device by kindleselect, it only told me "pls connect ur device" omg. And I can't enter usb mode either, my kindle screen is always in black!
So how can I solve my problems, I had 4.0.0 kernel and now I only wanna enter fastboot mode. Thanks for your reading much! :iloveyou: