|If you are in vista you can go to your control panel...sound... recording tab.... |
Look at the list of devices and set priorities for each. If you don't see any devices and you know you have one, right click inside the window and check "show disabled devices". Maybe you accidentally disabled it or something similar. You can then right click on each device and enable it or "set as default" aka if it is plugged in use it.
Hope this helps.