Hey there,
I have tried for three hours to repeat again and again the hard reset and the procedure was fine (aka Red light blinking and then turning off the bts). 
But still, after the hard reset, the nanobts boots (red light) and then stays fixed on Orange. sad :(

Obviously with my other rugby-139 both ipaccess-find and BTSInstaller work perfectly, so I strongly  suppose that the problem should be more serious than a static IP issue. 
I have tried to delve into the manuals, but unfortunately, I didn't find nothing useful.

Maybe a good soul can suggest me something else to try before giving up (e.g. UART, JTAG, USB connector?!).

Thank you for the attention.
Cheers,
Luca

As suggested by you and Chris, I have patiently shorted 9+10 and the light started to blink RED. Subsequently I have turned off the bts and removed the shortcircuit.
However, after turning it on again, the situation is always on ORANGE stable/not blinking light.

Right now I am reading the manual and it says:
"LED_SELF_TEST, Orange Steady, From power on until end of backhaul power on self-test"

I am wondering what else could be the problem. Maybe the MacGyver's way to short-circuit didn't work properly. (I am going to look for a proper RJ-69)

I have also noticed that if I don't plug it into the router, the BTS shows a RED stable/not blinking light.
And as the manual says, it could be a bad sign (I guess):

"LED_SELF_TEST_FAILURE, Red Steady, In boot or application code when a power on self-test fails.

LED_UNSPECIFIED_FAILURE, Red Steady, On s/w fatal errors."

If you have other suggestions will be appreciated. Thanks.

Cheers,
Luca

P.S. Just to be precise, I have followed the standard pin numeration to find the 9-10 pins ( http://quatech.com/products/images/rj45_sds.gif )