Hi Laura,
As you have disabled the built-in Microphone, first lets try to set the Microphone as a Default Device and enable the same.
Perform the task mentioned below to set Microphone as default device and then enable it.
- Go to Start and click on control Panel.
- Click in Sound, then a new window will open up.
- In the new windows click on the tab "Recording” and right click in the window and click on Show Disabled devices.
- Now check if the microphone is listed there and highlight the microphone and click on "Set as Default" device.
- Now right click on it and choose enable.
Doing this will enable the built-in Microphone.
Check if the issue persists now.
Refer this link for additional information:
Tips for fixing common sound problems
http://windows.microsoft.com/en-US/windows7/Tips-for-fixing-common-sound-problems
Regards,
Divya R – Microsoft Support.