Only one side of the DDJ-RB is lit up

It's possible the USB port on your computer isn't providing adequate power to the DDJ-RB and thus it's not functioning 100%. Please try using a different USB cable, port or another computer to try and narrow it down.

An easy way to tell would be to connect it directly to an iPad charging brick (or other similar device capable of delivering 2A) and see if the startup sequence illuminates all the buttons and pads as expected. If not, then there could be an internal hardware failure and servicing would be the best bet if it's outside the return period for your purchase. You can find Pioneer DJ service shops in your region here.