  We present a phase diagram as a function of disorder in three-dimensional NbN
thin films, as the system enters the critical disorder for the destruction of
the superconducting state. The superconducting state is investigated using a
combination of magnetotransport and tunneling spectroscopy measurements. Our
studies reveal 3 different disorder regimes. At low disorder the (k_{F}l~10-4),
the system follows the mean field Bardeen-Cooper-Schrieffer behavior where the
superconducting energy gap vanishes at the temperature where electrical
resistance appears. For stronger disorder (k_{F}l<4) a "pseudogap" state
emerges where a gap in the electronic spectrum persists up to temperatures much
higher than Tc, suggesting that Cooper pairs continue to exist in the system
even after the zero resistance state is destroyed. Finally, very strongly
disordered samples (k_{F}l<1) exhibit a pronounced magnetoresistance peak at
low temperatures, suggesting that localized Cooper pairs continue to survive in
the system even after the global superconducting ground state is completely
destroyed.
