Internal mic problem my doing?

I have a MacBook Pro, mid-2010 model, Snow Leopard, OS 10.6.8, 2.4 GHz Intel Core 2 Duo, 4 GB memory 1067 MHz DDR3.

My problem is with my internal microphone. I Skype once a week with my daughter and until 2 weeks ago, the internal micrtophone worked fine. I had an issue with the MagSafe connection, which was repaired by the folks at the Apple Store. After the repair, my internal microphone no longer worked with Skype. I discovered today I can use an external microphone to create sound for Skype and for Sound Studio, but when I choose Built-In Input, I get no sound for either program.

I would rather not drag an external microphone around every time I want to use either program.

Suggestions for a fix?

Thank you.