  In two dimensional electron system in magnetic fields such that the Fermi
energy lies in high Landau levels and driven by microwave $ac$-field a
divergence of the Coulomb screening due to the Ryzhii photocurrent is
predicted. A model of magneto-transport with superposition of long range and
short range disorders is introduced. In this model the larger is the gradient
of the long range potential the smaller is the longitudinal
conductivity/resistivity. As a consequence a qualitative theory of the recently
discovered zero-resistance states is given.
