There are more than one singers/bands by the name Nicole:

1)Nicole (the band): Finnish metal band Nicole is one of the founders of the new wave of Finnish heavymetal. Instead of following the trends of the day, Nicole has kept it's style of music the same since the beginning and continued to develope it heavier and heavier every year And more symphonic. (official website)

2)Nicole (Chilean singer): Nicole (real name: Denisse Laval) is a Chilean singer, based in Miami. She began her career as a young child. Her first album, Tal Vez me Estoy Enamorando (Perhaps I'm falling in love) was locally successful, reaching Gold Status. Years later, the singer released Esperando Nada (Waiting for nothing), produced by Tito Dávila (ex Enanitos Verdes), which sold more than 75,000 copies in her country alone. In 1997, Sueños en Tránsito (Dreams in transit), produced by Gustavo Cerati, made her deserving of recognition in Latin America as a consolidated singer.
Viaje Infinito (Infinite journey), released in 2002, part of Madonna’s Latin label Maverick Música, received a Grammy nomination for best Latin Female Vocalist.
Actually, APT (apartment), produced by Jimmy Frazier and Nicole have been listened
successfully in the Chilean radios and MTV. (Si Vienes Por Mi (If you come for me)).
(official website)

3)Nicole is a German singer, she won the Eurovision Songcontest for Germany back in 1982 with the song Ein bißchen Frieden, since that time she remained quite popular in the german schlager scene.
Some of her other songs are: Dann küß mich doch, Als die Blumen weinen könnten, Papillon and many more