[Kindle Fire HDX 7" & 8.9" Q&A, Help & Troubleshoot] jjrizzelcincy:
try rebooting the device and go into safestrap recovery and when you hear the driver try to load in windows go to device manager,it should be listed as mtp under portable devices,uninstall that driver do not reboot,,unplug device and then plug it right back in it should try to load the driver as kind fire hdx but fails,when it is done check device manager for the kindle fire with the triangle on it and click update driver,then click browse my computer for driver software,then click let me pick from a list of device drivers on my computer,then scroll down until you see kindle fire click it and then click ADB ANDROID user interface and the click next,if a box pops up saying something about drivers might not be compatible just click yes to install,when its done you will have kindle fire in device manager and in adb it should say what ever you device is and then RECOVERY after in adb then you can push the files needed

which i would use this one

https://mega.co.nz/#!WlQliIgZ!-SxzW77e4m0S5e520uxvwf6EYrbDNb-yL7O5ElnrO5c

from this thread

http://xdaforums.com/showthread.php?t=2665683

when the bin file is done downloading make a copy of it and put it in your

platform-tools folder with adb and change the .bin to .zip,,then push it to your sdcard (adb push update-kindle-14.3.1.0_user_310079820.zip /sdcard)

THIS WILL TAKE A WHILE! so let it do it's thing and when adb says it is done and the file is pushed press on the screen,(which has blacked out by now),, swipe to unlock and press install, you should see the

update-kindle-14.3.1.0_user_310079820.zip file on the sdcard now,,if so great lets move to the next step...

now hit the back button and go to the home screen,,,press wipe and swipe to wipe it (just do the regular wipe and thats it) DO NOT REBOOT YET

hit the back button or home button to go back to the home screen,,,now press install press the update-kindle-14.3.1.0_user_310079820.zip file and swipe it

it will say checking md5 no md5 found skipping modem update, installing and when it says finished successfully reboot system and it will be back to stock needing rooted and the whole works again except safestrap will still be there when it boots back on,,just let it continue or press continue it may take a few minutes to load the color kindle fire screen like any new rom would take to boot the first time,, KEEP WIFI OFF AFTER REBOOT,,,safestrap will stay installed but you will not see the app in the app draw and you dont need it because it is still installed ,so just root it using this http://xdaforums.com/showthread.php?t=2542456

dont worry about the errors just do what it says and then install busy box and supersu then do this http://xdaforums.com/showthread.php?t=2618158 and reboot the device one or twice,,after that download this http://android.mydedibox.fr/thor-gapps-installer-1.zip put it on your sdcard and then reboot to safestrap and press install and press thor-gapps-installer-1.zip and swipe when its done just reboot

then you will need to change the build.prop to keep it from updating

hope this helps you, it is what i had to do when the same thing happened to me so i know it will work!! good luck if you need any help let me know