Doing and Irish stout fermantation has stopped after a day or very much slowed down temp change may have caused this? Would putting a heat blanket on the bottom restart it?
How are you determining that your fermentation has stopped? If you are using the airlock activity please note that you cannot rely on that to tell if fermentation is taking place. Although, if it is full of krausen, or has blown across the room, you can take that as things are going well.
Taking gravity readings is the only way to be sure that the yeast are doing their job. What is today's gravity vs your starting gravity? Also note that some yeast / wort combinations will do 80% of their fermentation in the first 24 hours then use the rest of the week to slowly settle into a final finished state.
Unless you cold crashed your ale to somewhere in the 50's (F) or lower, I would just let it go, and start checking gravity in a week or so. RDWHAHB