DELL
Malfunctioning of laptop & deny to replace it within warranty period

I purchased a Dell vostro Laptop otag no H4DBN1 on 29 th Nov within 1 month of purchasing I am facing problem during operating my Laptop, its display become white .3 times I visit DELL CUSTOMER SERVICE CENTER they keep my Laptop for 7 to 10 days each time, but the problem still same. Last time I told them to replace it as it can not work more than 10 days without creating the same problem, but they denied. SO i would like to request you to help me replace my poor laptop within warranty period