I opened up my set to investigate and found that the small cartridge fuse had blown. Usually there is some reason for such to happen however, I replaced the fuse (calls for a 6.3A 250V on my set) and the set is working again. Actually on my set, I did not have the actual 6.3Amp fuse and I'm currently operating with a 5Amp fuse which is easier to come by. They are used for some of the Christmas light sets; its even a good time of year to find them! The fuse should be replaced with the correct one and as soon as I locate one of the 6.3Amp fuses, it is my intention to replace it, or I may wait until this one blows which I will expect much easier than the other. It is not really a problem putting a smaller amperage fuse in but you should never replace it with a higher rated otherwise you may take out something much more costly than a fuse if there is problems. "Good Luck"