Temps and light cycles go hand in hand, just like in the wild. When daylengths shorten and it gets colder, many colubrids will think hibernation is at hand, and eat little or nothing. When it gets warmer and days lengthen, an adult's (or even sub adult's) thoughts will turn first to food, then to love.
I have had some success with customers' nonfeeding snakes by getting them to put a strong light above the cage (be sure it doesn't overheat the cage) and leave it on for at least a couple of hours longer than the sun is shining. But not all night - you wouldn't want a light on you all night either, lol!
Try to mimic the seasons, just adding a couple of hours if you need to fool the snake into thinking that spring is already here, and it is time to eat. It may or may not work, depending on other environmental factors, and also depending upon the reason your snake is not eating in the first place.