I think there is a lock file that terminates the MongoDB. You have to remove the lock file that is present and then run your repair command. after the repair command, restart your MongoDB.
For removing the lock file:
sudo rm /var/lib/mongodb/mongod.lock
sudo mongod --repair
Start your MongoDB.
sudo start mongodb
sudo service mongodb start
After that kindly check the status of your MongoDB with the help of the following command:
sudo status mongodb
sudo service mongodb status
And then at last just start your mongo shell with the help of the following code: