When I type mongo it gives me error:

MongoDB shell version: 2.4.14
connecting to: test
Fri Dec  9 11:20:22.550 Error: couldn't connect to server 127.0.0.1:27017 at src/mongo/shell/mongo.js:145
exception: connect failed

When I start the project, it says that failed to connect to server [localhost: 27017]

I was working before but when another app was deployed to server (that also uses mongodb) it stopped working.

I installed mongodb again but no success. :(

Could anyone tell me what is the problem?