There are 2 case possible:
1. If you are running Hadoop version 3.0.0 then let me tell you that there was a change of configuration and http://localhost:50070 was moved to http://localhost:9870
2. If you are running Hadoop version 2.X, then what you can do is just stop all the daemon services, format the name node and again restart the services.
Following are the steps:
Step 1 : bin/stop-all.sh
Step 2 : bin/hadoop namenode -format
Step 3 : bin/start-all.sh
Hope, this will resolve your issue.