Ganesh,
The zero price in the task list is standard. The order will re-calculate the price using the current value when saved.
So the question is why IP31 isn't working...
Have a look at these OSS Notes:
http://service.sap.com/sap/support/notes/1767525
http://service.sap.com/sap/support/notes/2042428
Can you also send a screen-shot of the IP31 data which includes the material above.
PeteA