dell venue 7 3740 Table is not working

I have bought dell venue 7 3740 tablet last year. But due to some hardware issue they have replaced my tablet with new two month ago. Now that tablet is also not working. Everytime getting switched off automatically. And when m trying to switch on only Dell logo is displaying after that blank screen. I asked service center guys they have told me to bring that to service center. I have given my tablet to service center guys. They kept that tablet for 10 days and now they are telling they cant fix the problem. What the  is this. After keeping so many days they also not able to fix the problem. Also they are asking Rs. 500 money for that. Dell guys given me new tablet but only in 2 month that is also not working, how they are making their product. People are buying Dell product, because we have faith on you. but people will loose trust, if we find issues in products like this.