[Q]Restore failed + install ROM failed in Recovery topic

Hi everyone,

I was helping a colleague put CM11 on his Kindle Fire HD. 7", was following this process for the complete install and everything was going fine until I tried to install CM11.

Here's what worked
- Rooting
- Downgrading in 7.2.3
- Installing TWRP and second bootloader using this video (details to XDA threads used in comments).

Here's my issue: installing the rom went fine. I went with cm-11-20141112-SNAPSHOT-M12-tate.zip from the official CM site then the Google Apps. When I rebooted, it loaded for a while and got stuck with the blue logo (2nd bootloader). After a while I turned it off because it looked like it was bootlooping, went back in recovery, tried to install it again and here we are:

- installing anything fails
- trying to restore my nandroid backup fails
- ADB sideload doesn't work

Any idea how I could get out of this mess? I don't have a factory cable, my ADB drivers should be working and I managed to use fastboot during the installation but now it doesn't seem to work well.

Thanks in advance, if you need any precision let me know.