Why does 98 Ford Taurus with 68000 miles air conditioning and vents stop working and blow hot air?

Go look at this awnser,,, http://wiki.answers.com/Q/Why_can%27t_I_get_hot_air_or_cold_air_in_my_1997_Ford_Taurus_the_heater_core_hoses_are_hot_and_the_air_condition_pipes_cold