It is apparently common to have those strings of christmas lights malfunction (not turning on) after a short time (like one usage).
While the two common suspects are light bulbs (just need to replace the burnt ones) and fuses (the two fuses located at the male plug - push the very inconspicuous cover outward to reveal the fuses inside), my case at NYGC was the fuses.
The burnt fuse is darker. They threw out 5 strings of lights, and each string has one fuse blown, which I suspect is a normal thing, so I could 'fix' only 2 strings. By taking out the working fuses from the other 2 strings to replace the burnt fuses of these 2 strings. Leaving those 2 strings with 1 burnt fuse each and the 5th string with 1 burnt and 1 working fuse.
All thanks to this site for the How-To. Now all I need is to go buy those other fuses (125V fuse 3A Max.).