The battery is dead didn't realize until turning the key and no power on battery and ignition key want release and come out

check battery and connections new doesnt mean free from defects key can lock in ignition when battery is dead can also release use a paperclip or a small screw driver under column will see a hole insert screwdriver up and push release and turn key to off and remove How to Remove Stuck Key from Ignition On the underside of the steering wheel cover, directly below the key tumbler, is a hole about 3/8". remove the plug that covers this hole, take a pencil or long narrow screwdriver, and push it up that hole until you can feel the solenoid weight. This should allow you to remove the key. http://www.automotiveforums.com/t927962-_97_bravada_that_won_t_start_stuck_in_park_key_stuck_in_ignition_.html

Have the BCM tested. Also we need make, model and year to give correct assistance.

have to replace the failed battery

Hello, I would test the Ignition switch. There are contact points inside the switch and actually both the Run and Start positions on the switch put power to the coil.

If you disconnect the power wire at the coil (ignition post) you can test the wire from the Keyswitch.
Then unplug the Tickler wire on the starter Relay and the starter will not turn while you test the Keyswitch.

Hook up a testlight or voltmeter, get in the cab and turn the Keyswitch to Run and I'd bet the ignition wire is dead. If there is steady power at the ignition wire, either your coil or Module is bad.

When you turn the Key to Start, it should have power at the Ignition wire and I also bet it is dead until you get that bounce of power when you release the Key.

Make sure you have one working ignition key and all remotes for the vehicle.

1) Close all vehicle doors.
2) Insert the key into the ignition.
3) Hold down the power UNLOCK button on the driver’s door panel-continue to hold down until instructed to release in step 9.
4) Perform steps 5 through 8 in fairly rapid succession.
5) Turn the ignition switch to the ON position (as far as you can go without starting the engine).
6) Turn the ignition switch to the OFF position.
7) Turn the ignition switch to the ON position.
8) Turn the ignition switch to the OFF position.
9) Release the power unlock button on the door panel. The vehicle will lock and unlock the doors automatically.
10) Hold down the LOCK and UNLOCK buttons on the transmitter simultaneously until the door locks and unlocks. This step may take up to 30 seconds.
11) Repeat step 10 NOW for each additional transmitter (including any existing transmitters).
12) Turn the ignition switch OFF then to the ON position in order to exit the transmitter programming mode.

You need to get the battery charged enough to have the key's to release from the ignition switch. Take care that you do not damage the ignition switch over a simple boost to the battery. There is a micro switch on the gear shifter that signals the ignition to release the keys, but with no power to the gear shifter switch, the key's will not come out. Good luck and hope this helps, boost the battery or charge it enough to power the electrical system to the blazer and your should be able to get your key's out of the ignition. Keep me posted, be glad to answer any other questions you may have. 

If the battery is dead, the ignition keys will not release from the ignition. If there is no signal from the transmission shifter that it's in park since the battery is dead, then the ignition lock will not release the keys.  After charging the battery or jumping the blazer to start it and the key's still will not release, try this. 
There is a "plunger" as part if the ignition. Under the steering wheel there is a small removable cap that you can take off and put a small screw driver up into and press the plunger in and it will release the key. Good luck and hope this helps, Keep me posted be glad to help. 

1. Close all doors
2. Insert key into ignition
3. Hold down the power UNLOCK button on the driver's door panel, continue to hold down
until instructed to release in step 9.
4. Perform steps 5 through 8 in a fairly rapid succession.
5. Turn the ignition to the ON position (as far as you can go without starting the engine.)
6. Turn the ignition to the OFF position.
7. Turn the ignition to the ON position (as far as you can go without starting the engine.)
8. Turn the ignition to the OFF position.
9. Release the power UNLOCK button on the door panel. The vehicle should respond by
door locks locking and unlocking automatically. (If locks do not cycle after you let go,
not before you let go of the unlock button, then the vehicle has not entered programming
mode and you must start procedure over. Remove key from ignition, open drivers door
and return to step 1 ). If the locks do cycle automatically then proceed to step 10.
10. Hold down the LOCK and UNLOCK buttons on the remote until the doors lock and
unlock. This may take up to 30 seconds.
11. Repeat step 10 NOW for each additional remote. (Including any existing remotes).
12. Turn the ignition to the ON position to exit the programming mode.
13. Test remote(s).

CHECK THE BTSI SOLENOID ON THE SHIFT LEVER, IT MAY HAVE BROKEN.

If I understand you correctly your saying that the engine will crank on it's own when the key is not in the ignition? If this is the problem you have a warn switch with sloppy connectors that are shorting out between each other. Another remote possibility is a short at the starter solenoid.