Check and or replace your starter solenoid.
Most commonly, it's the starter or the starter was wired wrong when it was installed. More rarely, it can also be the keyswitch or even a bad gear on the flex-plate.
Your starter has gone bad and will need to be replaced unless you can take the starter to an automotive electrician and he may be able to fix it.
A starter will not disengage if the ignition switch is stuck or if the solenoid has jammed. This will cause the starter to constantly receive power.
The starter solenoid is located on top of the starter. It is the small cylinder attached to the starter. It is a part of the starter which can be replaced/repaired independent from the starter itself.
the starter cellanoid needs replaced.
Take the steering column housing off (usually held by 4 screws from the bottom) and remove the starter cap from the back of the ignition cylinder. In a Nissan, the ignition cylinder usually has a T shaped pin which turns the starter. if you can start your vehicle by turning the starter cap with a screw driver, you probably don't have an issue with the starter.
First of all you need to check the key ignition cylinder (it's where you put your key). Most likely it has to be replaced. You need to make sure that ON position does not trigger the starter. Only START should do that.If the cylinder is fine you will need to check the starter relay.
I would suspect a defective ignition switch. I would be more inclined to believe it was the starter relay/solenoid thingy i used to have an old amc eagle. and it did same thing starter wouldn't disengage. I replaced the solenoid/starter relay and it worked fine after that.
your ignition switch is hanging up in the crank position.
Disconnect the battery...
Why is Infinity G20 1995 occasionally not starting. I have to put it in neutural to start.
I replaced the starter but it makes a grinding nose how do i fix it