My 2000 Camaro z28 wont turn off. starts just fine but when i turn the doing the same thing key to off cr is still running. Just replaced the ignition lock cylinder and still

frist off is the cat still on the car? if not you have to get rid of the computer or bypass it becouse yhe computer runs all most everything.i had a 85 Z28 that would do that got rid of the cat douled it off but car ran bad or not at all took out the computer ran great after that

A couple of things can be the cause. You could have an issue with your battery connection, or your ignition switch is dead. Ignition switch issues tend to kill all the power to the car. They can go without warning. It's located on the driver's side on the steering column.

whole different ball game ,changing the lock and cylinder is not that bad if you have the tools,you can rent them at Oriellys

You might be experiencing a problem with your Vats security system. GM installed these anti theft systems on almost all of its cars in the 90's. (that little black chip in your key) They are known for turning off starters and injectors. Check out this link for symptoms, explanation of how it works, and solutions to the problem that you can do yourself. Hope this helps. http://vatspasslockpasskeysecurityhelp.yolasite.com/

Sounds like a battery cable problem. Check the battery cable terminals for corrosion and tightness. If those are fine, have a load test done on the battery.
Here is some troubleshooting tips:

Battery terminal connections loose of corroded. Check the cable terminals at the battery; tighten cable clamp and/or clean off corrosion as necessary.
Battery discharged or faulty. It the cable ends are clean and tight on the battery posts, turn the key to the On position and switch on the headlights or windshield wipers. If they won't run, the battery is discharge.
Automatic transmission not engaged In park (PI or Neutral (N).
Broken, loose or disconnected wires In the staging circuit. Inspect all wires and connectors at the battery, starter solenoid and ignition switch (on steering column).
Starter motor pinion jammed in flywheel ring gear. II manual transmission, place transmission In gear and rack the vehicle to manually turn the engine. Remove starter and Inspect pinion and flywheel.
Starter solenoid faulty.
Starter motor faulty.
Ignition switch tautly.
Engine seized. Try lo turn to crankshaft with a large socket and breaker bar on the pulley bolt.
credit: https://www.wc-autoparts.com/blog/trouble-shooting-no-start-condition-19932002-camaro-and-firebird/

No spark could be 3 things. Power to the coil is not there. Coil is bad. Or the chip in the distributor could be bad. Could be another possibility but it's easy to check. Remove the cap and before you pull off all the spark plug wires. Use some tape and label which location they where and number the cap so you can replace them after. Once the cap is off have someone try the key and make sure the rotor I turning. If it does not you may have a broken pin on the distributor shaft. My guess it may be the chip under the rotor which is a couple wires and screws. There may be 1 other thing if your car has a low oil sensor. Check the oil and add if needed.

Fuel pressure? Do you hear the fuel pump running? Read the codes to see if ECM is still alive. Do you have spark at the plugs? Remember all motors need 3 things to run air, fuel, and fire at the right time.

be more specific... won't turn over, turn over but won't start, do you hear a clicking noise?

it might be the optispark harness wire.it starts and runs good. once u turn it off its hard to turn back on?

could be map sensor or mass air flow sensor.