finding serial number



thanks for the response, i have the reciept but there is no serial number on it and could you please explain whom should i give the proof of purchase.... thank you
 
The vendor that sold you the laptop; it's name should be on the receipt. They should have a record of the sale, usually when they scan the product at check-out the system enters the serial number.
Another possibility would be the documentation/manual that came with the laptop. It could be noted on that somewhere (as well as the warranty card). It is worth checking all these possible locations, if available.