You can try Rock Salt to melt through the ice. Hot water will also melt the ice, but depending on the temperature outside this could be messy. As far as preventing this from happening in the future is concerned, there are a few steps you can take. First, make sure in the fall before the snow falls your gutters and downspouts are clear of debris. Also, make sure that your insulation in the attic is properly installed. If the insulation is not properly installed, heat may be escaping to the roof. The heat can cause the snow to thaw and freeze which may cause an ice damn. Your last defense is a heated element which would be installed on the roof commonly called Ice Melt Cable. This will heat and melt the snow and ice.