why can’t my family hear me on video message but i can hear them?

i tried windows live messenger for the first time yesterday with my mom & dad. I could hear them perfectly but they could not hear me. i also tried it w/ my sister and same thing. i did a test video on my dell webcam and recorded myself speaking and played it back. could hear everything fine. can someone tell me if i am doing something wrong on my end. i also checked my "sound" on computer and it states under recording that my internal mic IDT High Definition Audio CODEC default device and Microphone/Line In IDT High Def Audio CODEC default communications device. Do i need a Microphone/Line Out? if so where can i find that. Please help! Thanks