Hi Mitch, welcome to iFixit Answers.
A magnet located a the left edge of the display enters in contact with a sensor located on the battery charging board (under the top case) when you close the display, this action triggers the machine sleep function. If your display is a little twisted there could be a gap between the two components causing a bad contact and the macbook sleep issue. Check if your display is closing firmly to the top case. There could be a hinge problem. Was the macbook dropped ?