Did you set your USB microphone as the default recording device?
If you didn't, that maybe the reason.
Go to:Control Panel\All Control Panel Items
Then Sounds and click on the Recording tab. All your audio input devices must be listed there. Right click on the preferred one and select the device as default and try the Sound Recorder again.
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My Computer
At a glance
Windows 7 Ultimate Service Pack 1Intel(R) Core(TM)2 Duo CPU T6400 @ 2.00GHz3GBNVIDIA GeForce G 103M