What is your laptop? Have you reinstalled windows after installing a new gpu? It's not needed but it's recommended in order to get a 100% of potencial. You can also use this program to uninstall the current drivers.: http://www.guru3d.com/files-details/display-driver-uninstaller-download.html
After that install the newest drivers from nvidia website. Check your laptop wattage. What your battery is capable off it might be the deal. If it is correct in order to handle it than there is a gpu problem. What was your old gpu? Run heaven benchmark for me and paste screenshot.