2001 F150 Does not crank or turn over

I was going up a hill, the trans shift to a lower gear, the rpms naturally went up... all normal. But the engine went well beyond the normal rpm's, when I noticed it was hitting about 4000... then the engine died. I did not hear, or did not notice, any popping or loud banging nor was there any noticeable smoke. Now when I try to crank it I hear one initial click and it does nothing else. All the electrical gauges come to life as they should but nothing else. The battery is 2 years as is the alternator. One small detail... while it has run very well all these years is does have 425k on it. What might I be looking for as tot he cause of it not turning over or cranking? Any help would be appreciated. Thanks, JMR