Like Stinky already said, give them a few weeks before discarding. A lot of the seeds have thicker hulls (as mentioned) and others can remain dormant for a few weeks even when in ideal germinating conditions. You said you cracked it open and the innards looked intact (at least enough to discern a tap root from the rest), so it's possible it would have germinated.

As also said by Stinky, higher temperatures run the risk of fungus and seed-rot. My friend throws his in a wet paper towel, into a plastic baggy, into a dark canvas bag (for light protection), and then on top of the ballast for a 4ft. fluorescent. He gets anywhere from about 70-100% germination success on recently purchased (so presumably fresher) seeds.