  Using numerical simulations we studied the long time relaxation of the
hopping conductivity. Even though no modern computation is able to simulate the
behavior of a large size system over minutes or hours so as to observe the
relaxation, still we have been able to show that the long time relaxation and
aging effect observed in experiments can be explained in terms of slow
transitions between different pseudoground states. This was achieved by showing
that different pseudoground states may have different conductivities and that
the dispersion of conductivities is in agreement with the experimental data. We
considered two different two-dimensional models with electron-electron
interaction: the lattice model and the random site model, corresponding to
``strong'' and ``weak'' effective disorder. For the lattice model, effectively
strong disorder, we have shown that the universality of the Coulomb gap, which
is responsible for the universal Efros-Shklovskii law for the conductivity,
suppresses the long time relaxation of conductivity since the universality
strongly decreases the dispersion of conductivities of the pseudoground states.
