Fallout 3 dcl??????????

ok i am so confused. i purchased fallout 3 dlc, mothership zeta, and it says i have the dlc! it says i validly purchased it!! but when i go to the wastelands to get abducted, i only get the radio signal. the radio signal has not yet become a quest yet. how do you start the quest from the ominous radio signal??? because mine wont get the ominous signal and is acting like i didnt purchase the dlc. srry if i get repetitive/confusing. i am really tired