Solar lights use a small photovoltaic panel. When the sun shines on them, electricity is generated, storing power in a small battery bank. When a solar lights fails to light up, there are a couple of reasons for this. It only takes a few minutes to get your lights up and running again.
Remove the battery cover, if there is one. You may need to unscrew this.
Remove the old batteries and replace with new ones, if necessary. You will need to place the solar light in direct sunlight for at least two or three days to charge the batteries.