Start with something simple. Remove your battery cables and clean them / remove your ground cable and clean it and the block attaching point / remove the wires to the solenoid and clean them. If you have the "clicky fix" on your solenoid remove the ground wire and clean it and the grounding point.
If that doesn't work then get out the OHM meter and touch the battery posts. to see if your battery is discharging. If it still won't start I would guess that your solenoid is shot.
Does it click or anything?
Tux...