What do I do if my 2001 ford f250 cranks but wont start?

The thing most people do when their 2001 Ford F-250 cranks, but doesn't start, is call a friend that knows about cars, and sees if they'll lend a hand. Or, maybe, search on the Internet: Hi! Let's see if we can be that friend for You. The most obvious thing, of course, is Your battery. It's possible that You've got enough juice to start cranking, but not enough for the starter to actually turn over. Fixing this is simple: Charge or buy a new battery. You may also have a problem with the starter itself, which is likely for a twenty some year old vehicle like Yours. Other things to check are going to be the fuel pump relay; see if You've got any blown fuses. Additional culprits for this are the fuel pump and the fuel filter. Probably the weirdest reason You'll encounter for this behavior is that the key tumbler isn't making good contact; listen to see if the fuel pump engages when You wiggle the key when it's in the key-on, engine-off position to test for this unlikely scenario.