Thanks for the advice. 

I tried to edit the Move_base.launch by replacing this statement from 
<node name="map_server" pkg="map_server" type="map_server" args="$(find
my_2dnav)/map/map.yaml"/>
to 
  <node name="slam_gmapping" pkg="gmapping" type="slam_gmapping"/>

The program works very well initally but over time the system just crash. 

I was wondering whether it's because of the laptop limitation ?

My current laptop spec is 
core2 Duo with 2G ram and 128mb  dedicated graphic card

with thanks,
Zhiping
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