I assume by 4% you mean the gravity was about 1.030? We generally don't use the % scale. It just tells you thevalcohol potential if you ferment to 1.000. Since most beers don't go that far, it doesn't mean much.
I don't know your recipe, but if it was all simple sugars, it should go down below 1.000.
Unless the brew actually froze, the yeast will be alive. By dropping thectemp, thevyeast went dormant and dropped out of suspension. Keep the temp up, and gently stir, and leave alone, and it should start up again.