Touch screen and cold, dry fingers
Most touch screens are capacitive - meaning they detect the change in capacitance that is introduced by touching them. Insulators generally do not introduce a large enough change in capacitance to trigger the touch screen. So if your fingers are turning to papery stumps somehow, you wont be able to trigger it. This has nothing to do with the temperature of your fingers, but everything to do with the moisture and oil content on the surface.