I recently bought a brand new Seasonic 1250w power supply to upgrade from my old 1000w Thermaltake. When i installed it my computer would not turn on and i could see the led's on the mboard light up then turn off. It will work sometimes with only the cpu and mboard connected but never when i connect the video cards. I tried my old power supply and everything worked fine. Am i safe to assume i received a defective power supply or can it be something else.