We present a model of DNA for use in computer simulations; This model is simple enough to allow long-time large-scale dynamics simulations, while, on the other hand, it is sophisticated enough to describe both double stranded and single stranded DNA and the transition between the two. We employed our simple model in the simulation of denaturation of double stranded DNA helices using Langevin dynamics. These are the first simulations of its kind of DNA denaturation. We have studied the melting behavior for several short double-stranded sequences of different composition. Duplexes of different lengths were considered, and also base pair mismatches were included in the study. Results are in good agreement with experimental data.