Malfunctioning power button

I bought a Vostro from an authorized shop in Vietnam and was promised to changed a new laptop if I found any hardware errors within 30 days. I used to be extremely regreted not checking it carefully before bringing home. 

Right at the first time, I had unpleasant experience with power button when I had to press two, three, four times to turn on my laptop. I brought it back to the shop and reported my issue. They acknowledged my complaint, however they said my laptop would need sending to Dell service center to check. If Dell confirmed it was their error, shop would offer me a new one. After a week, I was called to pick up the orginal laptop with hard-to-accept explanation: Dell denied this error, they blamed malworking power button on newly used laptop and said it would work correctly after time. With that reason, I was not offered a replacement. They even did not fix this error for me. 

I am under impression that I was treated as a kid: spent over USD500 to buy a malfunctioning product, wasted a week to wait and then don't know how long to wait more until it work correctly. What happen if it do not? Who will guarantee for me? Now, I still have to press many times and wait for a century for my laptop to turn on. No word can express this upset, unpleasant feeling. DELL, why are you irresponsible to produce below standard product and make customer run the risk? IF YOU CANNOT DO BETTER, LET OTHER DO! This is my last Dell laptop in life. So so disappointed!