My most probable response would be you need to fine some additional drivers. If you can find a Win 7 legacy driver for your system you might try that. If all else fails and you cannot get it to work, you might try a Vista driver.
If you open the sound, recording window, and right click, you might try "Show Disabled Devices" and "Show Disconnected Devices".
Have you tried other type of microphones? I have never used skype, so there may be something with it that needs updating.