Definitely a defective screen now... Go back to the place where you get the replacement done and ask them to rectify it. If you didnt drop it or whatever, then the screen replaced wasn't a good one for sure. Have a good day.
Laptop not turning on could be due to Motherboard or RAM issue. But before confirming that... Try a power drain first. Press and hold the power button for 1 Minute. Then try to turn it on. Just sharing these base on my experience. Hope it helps.