People are unable to hear me through my mic

Hello,

I have a Toshiba L500-1QK. The program running is Win7. My problem is whenever I use Yahoo messenger or skype nobody is able to hear me while I can hear them. When I chat to my friends they tell me that they can just hear the first word then nothing. My mic is working probably when I use it on an office computer but not when I use it on my laptop.
I have the Audio HD Realtek. I made sure that everything is working. the volume is ok and so are the speaker but still the problem persists. Please help me.

Thanks