I have a 2003 Cherokee sport and the key wont turn the ignition

SOURCE: 1998 Jeep Cherokee Sport Ignition Lights Come on but wont crank

Try putting the car in neutral and starting. If its a manual trans it might be the clutch pedal safety switch or it may be something as simple as a loose battery connection.

SOURCE: 1998 jeep Cherokee Sport wont start

Give us more info. I will assume your past any battery issues so I won't ask. Do's it ever start or are you down and out?

SOURCE: when new battery is connected starter whirs

Sounds like the starter solenoid is stuck on, most likely need to replace the starter, sometimes what can be done is tap the solenoid with a wrench or a small hammer and it may come loose, if it stops i would still recommend replacing the starter because it will happen again 9/10 times. Also check the wiring to the starter and make sure the start wire is not shorted or installed improperly. If there is constant voltage at the smaller start signal wire, the problem is somewhere in the wiring or the keyswitch.

SOURCE: key wont turn over in my 1999 jeep cherokee sport

If the key is seemingly mysteriously prevented from being twisted to the "Start" position in the ignition, it is probably due to the transmission not being fully in "Park" (or in neutral or clutch fully depressed for a standard transmission).

The ignition switch is will move to start or not turn the starter when it is not in the correct position. Pull the shifter fully into the Park position (or in the case of a standard transmission - out of gear & press the clutch to the floor). It may be difficult to do this if you are parked on a hill or if there is some other issue with the linkage between the shifter and transmission. In any case, the shifter should click into position when fully in park. If the car has a lot of miles on it - the switch and linkage may be worn - and you'll have to "jiggle" the shifter back and forth to find the spot that allows the starter to turn.

It may also be a dead battery. The lights and chime require significantly less power than starting the engine does. Turn on the high beam headlights, air conditioner and set the blower fan to high. Then tap the horn. If your car can't do all this at once - the battery could be ready for replacement. Try to get a booster or jump start.

I hope this helps - good luck!