Handler is not starting activity everytime

Handler is not starting activity everytime

I have made an handler in a service which calls an Activity to generate
popup. It works fine when any activity of my application is opened.But
when activity is not opened that time it starts my popup activity only
once . I have checked the code by debugging every time handler invokes the
code of starting that activity but activity is not generated. But if any
activity of my application is opened then it works fine.
I am using FLAG_ACTIVITY_NEW_TASK flag since i am starting the activity
from service. Is there a problem of context.
Thanks in advance