Alienware 15 R3 fps drop after 10 minute

I bought  Alienware 15 R3 a month ago. First 3 week there is no problem about product but last week i cant play games like R6,Overwatch... First 10 minute there is no problem about fps but after 10 minute fps goes 0 for 2 sec than it became normal fps and after 20 sec fps goes 0 again. I tried everything about software. Updated Nvidia drivers , restored pc, installed recommended drivers which on Dell support.Also GPU heat between 75-90 in game.I checked it with GPU-Z, in each fps drop perfcap reason is pwr. Nothing happened. So i called Dell Turkey support. We did hardware test and they say  "Nothing wrong about your hardware, its about software". They said "restore pc,update drivers,..." But i already done that and i need quick solution. They say "We dont know anything about this problem we need to look at it, we will send you and email".I just bought it a month ago, it's new and i need it for my school. I checked internet, absolutely no solution. Please help me. I have GTX 1070 with 7700HQ on my AW.