Is it a Corny keg? Did you pressurize it at all while you were waiting for it to carb? The lid won't seal on many Corny kegs without some pressure. No seal = no pressure = no carbonation.
Wow a whole pint of dextrose? You should only need appx. 2/3 cup to make mad carbonation in a 5gal. keg, or is this a sanke? Do not put in more sugar, I would try force carbing.