The power rail you are connecting to is not powered by default. To supply 5V, you can install a jumper from one of the VREG or 5V pins in the nearby 2x6 block to the power rail. The source for the 5V pin depends on how you are powering the board. If you are only supplying power through USB, it will receive power from there, and if you are supplying power through VIN, it will receive power from VREG, which is the output of the onboard switching regulator (and can handle more current). Either source should work for those Sharp sensors, but if you want to add more devices, it would probably be better to use VREG.