K4 Can´t go into usb dowloader mode to debrick my Kindle

Hello everyone, first of all, sorry for my poor English. Let me explain my problem:

I have a Kindle 4 NT than suddenly gets stuck in the wallpaper screen and doesn't power on. I tried pressing the power button for 30 seconds and it rebooted and began to work OK. Then I powered it off and since then it has never powered on again. I tried several times to press de power button for 30 seconds (even for a minute) but no luck (I charged the Kindle for a couple of days to ensure it's fully charged).

I decided to use the Kubrick's live CD to debrick it but it remains in the step "waiting for device..."
I also tried in Windows (XP and W7 32bits) but the Kindle isn´t recognized and MfgTool doesn't show any devices.

So to sum up, this is the situation:

If I plug the Kindle in the wall charger, the orange LED turns on but it never turns green no matter how many hours I leave it charging.

The kindle not powers on.

I'm not able to get the Kindle into USB donwloader mode. The steps I follow are:
1) Plug the kindle into USB.
2) The orange LED turns on.
3) Press and hold the power button for 10-12 secs, and the orange LED turns off.
4) Then press and hold the DOWN button.
5) Release the power button, and the orange LED turns on again.
6) Release the DOWN button.
7) Nothing happens, the kindle doesn't go into usb downloader mode (Kubrick and Windows not recognize it).

Is there anything else I can do to recover my Kindle?

Thanks in advance.