Default Moto XT910 fastboot issue

Hello everyone. First post here, although from time to time I take a look here to see what's going on.
Is now a week without phone. I searched many forums, and Googled a lot, but no luck.

The phone is a Motorola Razr GSM (umts_spyder), XT910. It had installed Safestrap, I don't remember the version.
I tried some roms from time to time, installing them through the Safestrap.
The last one was SlimKat (4.4). I wanted to go back to MIUI V5, which was the one that I liked most of which I had proved, but the Safestrap tell me that the rom can't be installed due to space issues. Then I thought that I should delete some files.
Okey, that's when I make the mistake. Using the Safestrap built in File Manager, I deleted some folders that I thought are not essential. I thought they were remnants of application installations folders and stuff.
And after that, I rebooted the phone, and never woke.

I read guides on installation through fastboot. I can boot the phone in recovery, using -it seems- a factory recovery.
I have already the drivers for my phone from Motorola.
I tried RSD, Odin, and another script and stuff that I found on the web.
All the metods fails at the cdt.bin copy.
According to what I was reading after that, one cannot install an older version of Android from which it was last installed using fastboot.
Is this true?
If so, that means that I need to install a 4.4 fastboot rom on my phone? I can't find any.

Okey, that is the story.
Any advice will be appreciated. Due to my negligence and inexperience, my phone is now a cute ornament.

Thanks in advance for any help you can give me.
Best regards,
Francisco.

Edit: I was trying again, with other fastboots. No luck.
Is there a way to create a fastboot from a "common" rom?
I'm without phone for about two weeks.