40-45F sounds more like the conditions for lager yeast to do their thing. If you're making an ale, you're probably putting the yeast in an environment that will force them to hibernate. Unless your yeast conditions specify these lower temperatures, I would warm the wort up, probably to the 65-75F, but again, it depends on the yeast. That being said, I don't think you would've ruined anything, just slowed down the fermentation process, or maybe even stalled it. I would imagine by warming it up, you'll be fine.