No auido in skype

Hello,
I recently downloaded Windows 7 and tried using my skype, however, I was not able to hear my friend nor my friend could hear me. What could be the problem? It was functioning well few days back, but I noticed this problem after installing Windows 7. I could not hear my friend in MSN as well. They prompted me 'No audio & microphone attached', when I have an in built cam & mike in my laptop.

Kindly get back to me asap!!

Thank you