If for some reason your LED fairy lights are not illuminating, firstly check that they are plugged into a working 5v USB socket. If using a USB plug to plug into a wall socket, ensure the USB is slotted in snugy and correctly and that the wall swith for the socket is ON. If you are using a power pack, ensure that it is fully charged (charge it for at least an hour to test it). If the above doesn't resolve the issue, then the string of lights may be faulty. We have a fantastic quality record and each set is tested before shipment, but on rare occasions, these things can happen. Don't panic, we're here to help you and get a new working set of LED string lights to you as soon as possible. Please contact us at: hello@cableandcotton.com