Just an FYI-- the 770 needs no extra driver to make a keyboard work. Once you plug it in it will "just work". The first thing I would check is that the green and white (data) connections are connected properly; if they're swapped it won't work. I'd also verify that the 770 is really in host mode by plugging it into a PC (it should show the USB icon but the PC won't see it). Lastly, are you sure both the 770 and keyboard are getting 5VDC? The keyboard will likely blink the caps/num lock LEDs when it is powered up. I've had issues if the keyboard isn't getting very close to 5V. You can also try typing dmesg (as root) after plugging the keyboard in to see if it recognizes that something is connected.

Larry