Can you please try shutting down your Sandbox completely and then try restarting it again to see if it works.
Also please check if you are able to do SSH successfully to the Sandbox afetr it comes up?
1. SSH on port 2222 (For HDF sandbox port will be 12222)
# ssh firstname.lastname@example.org -p 2222
Enter password: hadoop
2. Once you are able to do SSH then can you try checking if you are able to access the Web Terminal?
3. Do you see any error while starting your Sandbox? If yes then please share the screenshot.
4. Are you able to Access Ambari http://localhost:8080 ?