Heya @Sai Manohar Boidapu
A few different suggestions to get the ball rolling:
1. Is the HFDS service and it's components shown as running from within Ambari? There should be a green checkmark next to HDFS and its components (Namenode, etc.)
2. If it is, could you then see if the namenode is up and running: ps -ef | grep -i namenode
Would you happen to have the latest HDP Sandbox (HDP 2.6.3)? https://hortonworks.com/downloads/#sandbox
The version you have (2.5.x) should work as well, just mentioning in case you're interested.
That said, how much RAM is being allocated to the Sandbox? By default it should be requesting 8GB from VirtualBox, was this changed? Could you try SSH'ing into the sandbox (ssh firstname.lastname@example.org -p 2222) and if that doesn't work, then into the wrapping VM (ssh root@localhost -p 2122).