Hi,

There are several possibilities:
1) first make sure that you use profile optimization (renumbering) with skyline solver, as this can dramatically influence the performance of the solver. Renumbering is activated either by running oofem with "-rn" option or by adding "renumber 1" to analysis record.
2) you may try to use sparse direct solver DSS, which is a part of oofem distribution. You have to compile oofem with DSS support. Then just add "lstype 4 smtype 8" to analysis record (for ver. 1.9).
3) you may also try iterative solvers, as they may be more efficient, especially for large 3d problems. This requires to configure oofem with  IML or Petsc libraries. Please note, that suitable preconditioning has to be used, particular type is difficult to guess, as this is problem dependent.

Borek