I can think of lots of reasons that the fermentation might not start. But there aren't that many that will cause it to get stuck after it has started. If there are preservatives in the dried fruit, it might not start at all. But once it has started, that is unlikely to be the problem.
Here are some things that come to mind that might cause the fermentation to stop once it has started:
* Hitting the alcohol tolerance level for the yeast
* Too little nutrients
* A change in temperature (e.g. moving to a colder location)
* Something added to the wine after it has started (e.g. fruit containing preservatives)
As
@IslandLizard said, cooler temperatures won't harm the yeast unless you freeze it solid. If it is too cold to ferment, the yeast might become dormant and restart once it warms up again. In that case, stirring might help get the yeast started again. Look up the datasheet for your yeast to find the optimal fermentation temperature.
You should consider each wine individually. Using the OG an the current SG, what is the ABV? If the ABV is above a certain level (I think about 8-9%), then the yeast
cannot make use of nutrients and so adding nutrients won't help.
If you are not sure why fermentation has stopped you could try making a yeast starter. The goal is to get a healthy, active yeast colony ready to add to the wine. Rehydrate the yeast at the manufacturer's recommended temperature, prefereably using Go-Ferm. Then gradually add some your wine, starting with 50% the volume of the starter, then add enough to double thev volume again. Each time wait until you see clear signs of fermentation before you add more wine. After the 2nd addition you might want to let the starter work overnight. This procedure will help the yeast adjust to what is apparently difficult conditions. They you have a vigorous yeast colony to the wine. Dry pitching more yeast in a stuck fermentation is unlikely to make any difference.