Many writers use nor as a conjunction even when the negative state has already been established in the sentence. Savvy writers use or because the negative state carries over to the series. Consider this correct sentence, where the word no establishes the negative state:
Don’t hesitate to start a sentence with Nor. It’s a coordinating conjunction, and great writers have been starting sentences with conjunctions for hundreds of years. You can remember the coordinating conjunctions by referring to the acronym BOYFANS: but, or, yet, for, and, nor, so. You can begin a sentence with any of these. And you should.
Consult the Parts of Speech section of Grammar.com for a discussion of conjunctions, particularly the coordinating conjunctions and the correlative conjunctions. Click here for the beginning of that discussion.