Find the starter relay (it should be right near the battery, between the battery and the starter), remove the covers from the 2 battery cable posts on the relay then with the lanyard on the DESS post arc across the relay posts with a screwdriver... if the starter engages that way, then the relay is bad and needs to be replaced.
In all likelihood the starter relay has simply gone bad (the inside chars where the post butts are arc'ed over by an electro-magnet which operates the relay... I took mine apart to see why it wasn't working anymore, there was black char all over the post butts inside the relay). If arc'ing across the relay posts doesn't engage the starter then you'll have to pull the starter and get it checked (most automotive electric shops should be able to test it and repair it if needed). I'm betting the starter relay just needs replacing though, and that's easy you can do it yourself.
- Michael