in-built microphone problem after installing windows 7

just did the automated Toshiba upgrade/Windows 7 isntallation procedure and how have Windows 7 instead of Vista Family Edition. Only trouble, the in-built microphone no longer works. I can skype or record with my plantronics headset through a USB jack but not without it. Tried fiddling with the microphone settings by right-clicking on the speaker ikon, but have not succeeded in restoring the in-built microphone. Can anyone help?

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