How many keys do you have?
If 2, have you tried them both?
Is the battery fully charged - have you tried jump leads from another car?
When you turn the key to start, do the oil/ign warning lights go out or go dim?
I'd try a lead from the battery positive direct onto the starter solenoid (to the small terminal) - that bypasses the key switch and the wiring between the battery and the starter. The engine should now turn over.