RE: Inspiron 17 5748 does not recognize external microphone
If you still have it, plug it in and go to the Recording devices tab. There should be a new listing for a usb device. Make it the default recording device. If it does not appear in the list of devices then it is probably defective, or something wrong with the usb port. Also make sure that the recording program you are using to test the mics is set to use the usb mic.
I no longer have the headset, since Logitech said it was "defective", but I have ordered a Plantronics USB headset with good reviews and will try your recommendations above once I receive it. I am increasingly convinced that the computer headset jack is faulty or the h151 has too high an impedance to be detected.
Thanks again for all your help...