Perfomance drop when projecting laptop to TV

Hello, I was wondering if there was any reason or fix to my laptop performance and fps dropping when projecting to my Roku TV. The monitor of my laptop had been broken off so as a temporary fix i hooked my laptop up to my TV via a HDMI cord. Before this I could run games like “Half-Life 2” and “Fallout New Vegas” at a steady 30 fps. But once my TV is used as a monitor both of these games drop to unplayable frames per second. I was wondering if there were any settings I could change, or software I could install to help aid this situation.