Windows 7
I had been using my microphone with Skype for a while then it suddenly stopped working. It would give me a recording device problem in skype calls and the mic will not work at all anywhere else on the system. Also no green bars in the sound manager so it is clear the computer is not getting any sound from my mic, however the mic work on other computers.

So it looks like it is a software error. Nice easy fix! Re-install the sound drivers:

Note:
Make sure you have the drivers for your sound. Windows should be able to auto-install most but I cannot gaurentee you do not need them.

Uninstall:
Right click the speaker icon in your tray (Bottom right) then click recording devices. Click pretty much anything as they should all have the same driver but click a mic if it is there. For me I selected “Front Mic”. Click the Properties button at the bottom right of the window. Under the General tab click Properties again under the heading “Controller Information” for me this was “VIA High Definition Audio”. Under the General tab of this window click “Change settings”. Under the Driver tab of this Window click Uninstall. Now you have no sound at all!

Install:
Win 7 Orb > right click “Computer” > Manage
This will bring up a management window, on the left you want to click the “Device Manager”.

Right click on the sound section and click “Scan for hardware changes” … In about a minute or two windows should pick it up and install the default driver, If you have special drivers now would be the time to install them again.