try another usb port. sometime there are glitches with usb devices and usb 3.0 ports. try one of the older 2.0 ports. if your keyboard still will not light. make sure only the keyboard and mouse are plugged in. sometimes having an iphone or hub connected at post will pull to much power from the usb chipset and hang the usb ports. if another keyboarddfoes the same thing. power the pc off and use the clear the cmos jumper to clear the cmos..you may have turned off your usb ports.