Yeah, thanks a lot! ... the weird thing is that, after pushing the reset button, the battery was almost totally discharged, so I left the device charging again for more additional 12 hours, without getting the light lit yellow. Finally I disconnected it.
Another weird thing -probably related to the original issue with the new firmware- is that I noticed a general loss in light contrast, more evident when I try to read pdf, with random not-homogeneous definition of what is displayed by changing pages or browsing the GUI, especially with small size characters. I had not such a bug with the previous firmware. Any suggestion for that or should I open a new thread for it?