"Stereo Mix" is missing

I used Audacity 1.2.6 on a Windows XP for several years. Later, I updated to Audacity 1.3.0. All the while, I was able to use “Stereo Mix” as a recording device.
Recently, I updated the operating system to Windows 7, then installed Audacity 2.0 (from the .zip). “Stereo Mix” is no longer a recording option. I read through the FAQ here, and tried a few solutions that did not work. Then I found this page:
http://wiki.audacityteam.org/wiki/Updating_Sound_Device_Drivers
Which suggested that I find the manufacturer of my Sound Device and update the driver (under the assumption that the manufacturer’s drivers would be better than generic ones from Microsoft). However, my sound device is listed as being manufactured by Microsoft (it was RealTek before the operating system update), and no updates are available from Microsoft.
I am very frustrated and somewhat confused by the whole ordeal. Please, can someone tell me what has happened, and how I can fix it.
For general information, I had already tried to ‘show disabled devices’ in the recording tab of volume control. No devices appeared. I also still have all my XP system files in a windows.old folder on my C: drive.

To get the recordings back, you’ll have to actually be running WinXP, not just have the files.

If you’ve been through the wikis and instructions, you know that some newer machines can’t record internet music at all and that’s the way it is. You’re only solution is Total Recorder on Windows, for example, or other software packages, but that’s what it takes. Higher-end software makes its own devices and pathways independent of Windows.

Audacity doesn’t.

Koz

That suggests to me that you haven’t yet finished your Win 7 upgrade. Assuming that you didn’t change the soundcard when you upgraded to Win 7, your system has a Realtek soundcard but is not using the Realtek drivers. If you can get the Realtek soundcard reactivated you might get Stereo Mix back.

If your computer is a branded computer (eg Acer/Dell/HP/…) then check on the manufacturers web site for driver updates. Ensure that you get the drivers for the exact model number of your computer and the same operating system.

If your computer is not branded, then check the web site of the motherboard manufacturer. (If you take the side off the computer you should be able to see the make and model of the motherboard printed onto the motherboard. Take care not to disturb any of the internal connectors.)

Okay. I solved the problem. My computer is an Acer, so I downloaded and installed the RealTek sound driver from the Acer website. Stereo Mix reappeared (although it was at first disabled, that was an easy fix). The speakers gave me a little bit of quality trouble for a bit after that, but not long later, all was well again.
Thanks everyone here for your help.