I have sound everywhere on my computer but not in programs like yahoo messenger, paltalk, or aol messenger?

I AM RUNNING WINDOWS 7. You tube videos play sound, my cd player will play music, movies will play sound, the start up windows sound I can hear, but there is no sound when I'm trying to hear friends on yahoo messenger or paltalk, software programs like that? In windows messenger it says that the audio isn't compatible, and I right clicked the speaker icon, and went to playback settings and record settings and made sure everything was appropriately checked, and I fiddled around with the sound mixer setting options, and nothing seems to let me hear sound in yahoo messenger or paltalk. I have even gone into the properties of paltalk program and yahoo meseenger and ran it in a different compatibility mode, but still nothing, and I remember each step I did. Why can't I hear sound in these programs, but I can hear sound everywhere else? Any info will be helpful. thanks.