2 cups of sugar in 2 cups of water? too much sugar...the yeast likely cannot live in that much sugar.
more sugar doesn't mean better. 1 cup per liter of water, on average, is as good as you can get with bread yeast. buy champaign yeast and you'll get a little more bang for your buck...but it may not last as long and simply produce more CO2 more rapidly.
You'll need 65F temperatures, no colder, or your yeast will stunt too.