Update: I've tried to edit the config.txt file adding the "max_usb_power=1" line with no success, but I was using a USB power addon to power up the Raspberry using a USB Type A conector. The next thing I tested was to power the Raspberry using a MicroUSB cable directly from the power supply, and thanks to a huge luck, the USB capture device was listed! So, I don't know if the USB power addon is damaged or has a current limit, because I can't use the USB capture when that was in the project. So, in resume: My suggestion would be to power up the LEDs and the Raspberry from the same power source, and power up the Raspberry using a good quality microUSB cable. Now I'm playing around with all the settings for the videograbber like resolution, divider(or something like, that I don't understand clearly at this time), FPs(whi I've selected 30 but I'm dealing with te temps of the Pi to avoid damage). So many thanks to Lighting-guy77 who shared to me the usb power limit on the pi, and I think that solved my issue. Good luck for everyone!!