Hi Kaotip,
Have you had a chance to go through the Sandbox Virtual box setup guide?
http://hortonworks.com/wp-content/uploads/2015/06/Import_on_Vbox_6_08_2015.pdf
I noticed that you only gave the Sandbox 4GB of RAM and here is what the setup guide suggests:
RAM 4 At least 4 GB of RAM(The more, the better) If you wish to enable services such as Ambari, HBase, Storm, Kafka, or Spark please ensure you have at least 10 Gb of physical RAM in order to run the VM using 8 GB.
–Rafael