k well Pablo, seeing as nobody else besides Tango has been even remotely helpful, I'll see what I can do to help.
firstly, have you tried simply charging the device? or is it already charged? if it's already charged, try connecting the device to the computer, opening redsn0w, and then putting the device into DFU mode.
try that, see if it works. regardless of whether or not it works, tell me what happens please.