but things went wrong there when i next restarted the system i could not find the DB active icon( which is in green color ,shape is in drum shape) which is expected.
This happened because you chose to start the database manually.
I haven't worked with DB2 but generally if you go to the installed programs list and find DB2 there, there should be an option to start it.
Alternately you can go to the installed directory and look for something like DB.exe or start.bat or something similar. But caution: the second approach is not recommended if you are not sure of anything.
It would be worthy to wait for a more appropriate answer.