I'm guessing something like, "No me interesa, ni un tantito." Or, "No me interesa para nada." Take a look at: http://www.wordreference.com/es/translation.asp?tranword=not%20at%20all
Note: the verb interesar behaves exactly like gustar. No le interesa nada = Nothing interests him (or) Nothing interests her. It lives in that funky IO + V + S world (indirect object pronoun + Verb + subject).
Literally, the sentences would be Nothing is of interest to him (or) to her.
So, in DL sentence, nada is the subject.
La música moderna te interesa. = You are interested in modern music. (or) Modern music interests you. There is a bunch of these types of verbs, but do not look for them on DL. Unfortunately, they are few and far between.