  We study the scalar potential in supersymmetric (orientifolded) Calabi Yau
compactifications of Type IIB theory. We present a new mechanism to stabilize
all closed string moduli at leading order in \alpha^{'} by introducing
consistently fluxes. As usual we consider the dilaton and the complex structure
moduli stabilized by turning on three-form fluxes that couple to the F-part of
the scalar potential. Kahler moduli get fixed by the combined action of the
flux-induced scalar masses with magnetic fields of the open string sector, and
Fayet-Illiopoulos terms. For supersymmetric three-form fluxes the model is N=1,
otherwise the mass terms are the scalar soft breaking terms of the SM fields.
For the case of imaginary self dual three-form fluxes (ISD), the mass terms are
positive and the minimum at the potential is at exactly zero energy. We argue
that, under generic assumptions, this is a general mechanism for the full
stabilization of closed string moduli. The vacua depend explicitly on the
fluxes introduced in the manifold. A concrete realization of this mechanism on
type IIB on a (T^ {6}/Z_{2}xZ_{2}) orientifold is provided.
