I have the EXACT same problem with my Logitech c110 cam/mic. I did EVERYTHING and it doesn't work if i scream at the mic it registers and i can't figure why I have done everything. Install/reinstall sensitivity settings,everything. I can't get it to work.
I did that. Sometimes it did work for a short period of time. When I used another port "installing new device" etc popped up worked for a day then the same happened. When I run out of ports nothing could be done. If I scream to it it works. I installed and uninstalled everything twice. I went to all the possible option tabs. Nothing.
Please, run the DirectX diagnostics tool.
Go to Windows Start and in the Run box type dxdiag.exe and press the OK button. This will start the DirectX diagnostics program. Run this diagnostics and save the results to a file. Please, attach this file to your post.
Be aware that you will have to zip this file before attaching it here.
There is nothing in the diagnostics file that can explain the issue. Have you tried with a complete uninstall/reinstall of the Logitech drivers?
I know. I took a look at them too. I send it to you in case I missed something. Well guess what. At the 57th time I plugged it in and out it worked. Now it's ok. God knows for how long. Thank you for your efforts anyway.