The low temps will not hurt the beer, but probably has forced the yeast to completely stop working (if they ever even were still active). Simply warm up the beer to 68-70 F before adding your next starter with fresh yeast.
BTW, what type of yeast did you purchase and how are you going about making the starter for it? You want to be sure to pitch an active healthy starter that is currently fermenting at its peak krausen for best results. I would not be too concerned about the amount of yeast in your fermenter especially if the beer is under the 6 wk mark in terms of time fermenting.