Database 'neo4j' is unavailable. after importing data in offline

Hello I have installed latest 4.2.3 version of neo4j. the set up went well and password authentication also worked. I could run cypher-shell by resetting password from default neo4j. After importing offline a large chunk of data. I have restarted the neo4j db and then cypher-shell but it is not opening rather it shows
Database 'neo4j' is unavailable
I even tried chown on /var/ neo4j/ lib/data/databases/ permission but didnt happen. My offline importing was successful. .
kindly enlighten me to solve this

Hi kalyan
Please find the admin command that sets Neo4j as default user.After that you can try other administrative commands.
Thanking you
Yours faithfully
Sameer S G