  We use F-theory to derive a general expression for the flux potential of type
II compactifications with D7/D3 branes, including open string moduli and 2-form
fluxes on the branes. Our main example is F-theory on K3 $\times$ K3 and its
orientifold limit T^2/Z_2 x K3. The full scalar potential cannot be derived
from the bulk superpotential W=\int \Omega \wedge G_3 and generically
destabilizes the orientifold. Generically all open and closed string moduli are
fixed, except for a volume factor. An alternative formulation of the problem in
terms of the effective supergravity is given and we construct an explicit map
between the F-theory fluxes and gaugings. We use the superpotential to compute
the effective action for flux compactifications on orbifolds, including the
\mu-term and soft-breaking terms on the D7-brane world-volume.
