Nexus 7 2012 Hard brick after downgrade?

Hello guys! I come now to the point ..

I bought the Nexus 7 WiFi only for in-car use .. When I received it, had the CyanogenMod 12.1! so I decided to install the rom AUTODROID 1.2! I downloaded the ROM, install the .zip TWRP (latest version) and so I had a bootloop .. Restore backup done previously with TWRP! I am looking online and I see that making the dowgrade from lollipop kitkat, first I had to flash the rom original KitKat!

ADB and fastboot drain, drain the "ROM" (the right one for the Nexus 7 2012 wifi), reboot into fastboot mode and do the command .bat adb .. but something went wrong

"Fastboot.exe stopped working"

From here you have begun problems: recovery is no longer accessible, and restart I always brought to the fastboot mode! I had the bright idea to turn off the tablet ...

From here .. Black screen, fastboot mode is not available, recovery is not available, so I can not even give commands ADB .. When the connection to the tablet pc, windows gives me input connection, but during the driver installation I give me the error "Unknown Device" ..

I do not know what to do .. Can you help?

Can't flash any ROM on my Nexus 7 (2012) - bricked device

Hello,
First time writing on the forum so please tell me if I do something wrong :)
So problem is that I tried to flash the latest version of Paranoid Android on my Nexus 7 but I'm getting the error "Warning! No file-contexts" and the flashing gets stuck on the next phase which is "Patching system image unconditionally..."
My device is rooted and unlocked, and I use TWRP. Of course I wiped cache, dalvik, system and data before flashing the new ROM.
I thought that the problem was with the zip package, so I managed to download it again from my laptop and pushed the image with adb. Unfortunately, I'm still getting the same message.
I even tried to install another ROM (Chroma) but it didn't work either, still getting stuck at patching system image. At this moment I wiped the whole internal storage, which worked with my previous problem on my Nexus 5.
Issue's still there.
What should I do now? I can't boot because no OS is installed. Should I try flashing the stock Android version? Or will I get the same message? My tablet is bricked, only thing I can do is booting in recovery.
Thank you very much for your help!
Kind regards,
Sebastian

Unofficial build of CyanogenMod 11.0 for Nexus 7 (Wi-Fi 2012)

This is an unofficial build for all those who want to stay with CM11. The build is based on the pure CM code and does include the stagefright patches and other patches up to July 30.

It does run perfectly on my own Nexus 7. However, use at your own risk.

https://www.mediafire.com/folder/7yw...m3q24a2/shared