Our light strings use a fused plug in case of over-current exposure. You will find a little door on the plug that slides out to reveal the fuses. Using a toothpick or something similar, you can pry the fuses out and replace them with the extras that come in the little waxy white paper bag attached to the plug-end of the cord. The old fuses should have a smoky, greyish tint in the glass part of the fuse if they indeed blew.
In the event that you had this happen while you were installing the bulbs in your light string, these style fuses are intentionally made to be sensitive to spikes in current as to protect the bulbs and the wiring. When screwing the bulbs in, whenever possible, we recommend doing it with the bulbs unplugged or any light strip they're plugged into turned off, as a small amount of arcing can happen (between the hot terminal of the socket and the bottom terminal of the bulb) when screwing in bulbs to actively-powered strings, especially if you happen to be twisting a little slow at the moment it's about to make contact. That small arc can be enough to cause them to blow, so by making sure the light strings are off while screwing bulbs in, it should prevent this.
While replacing fuses from time to time is part of the holiday decorating game, rest assured it doesn't indicate anything wrong with the light string or bulbs, unless it happens again repeatedly immediately after changing them – which is exceedingly rare.
Fuse replacement is always the first step we recommend in any situation where no lights on the string lights up. If after replacing the fuses you still have trouble with your light string illuminating, please don't hesitate to contact us and we'd be glad to help further!
Need more fuses? Our fused light strings use 3 amp (3.6x10mm) 125V Fast-Blow Glass Fuses commonly available in the holiday decor department of big box stores around the holidays, but also commonly available online.