well if you have tried a 'working' mic on this laptop and you still do not get a response then it could be your audio drivers or worse the motherboard.
have you tried uninstalling and reinstalling the audio drivers?
check this link for the driver:
http://www.mediafire.com/?dg0cmmkm4y4
=== use the steps below to install the driver. i got the steps here:
F700 sound & mic -= WORKING=- ==========
Unzip to a folder.Run installer.If it errors use device Manager.
From Device Manager,right click "Audio Device on HD",choose Update driver,
No to connect,
Install from a list or specific location,
Don't search I will choose the driver to install,
In the list of common hardware types, scroll down and select Sound, Video, and Game controllers.
Remove the check from "Show Compatible Hardware" and click on "Have Disk".
Next...browse to the unzipped folder and choose the "WiSVHe5.inf".Ignore XP when it complains.
Reboot.