No start

The battery and starter are both new. It began acting up, cranking most of the time and then not. Turn it to the on position and everything comes on. Go to crank it, no sound except for the fuel pump doing its thing and nothing else. At first it was a security problem, which was easily remedied with another key from a nearby dealership. Now, it's doing the same thing, but the security light no longer flashes. Any ideas?