RZ19 0366 ring light won't turn on

My ring light won't turn on. I took it to best buy to see if they could fix it and it turned right on. Then I brought it home and plugged it into my mac and it worked for a couple of days. Now it won't turn on again. I've tried using an external usb plugin that I know works and it still won't turn on. Is there a specific usb that I should be using? If that is the case, I'm confused as to why it would work on my mac for a couple of days and then stop working again. I wonder if I need to replace the cord?