No stereo mix in vista 32-bit, used to work until reinstall. Help?????

Currently at my wits end.

I have windows vista 32-bit.
It was preinstalled when I bought this computer years back, and i've had it reinstalled professionally twice. Recently I reinstalled it myself using a genuine vista disc from ebay, just to start fresh, and it works fine - minus one issue. No stereo mix! I need stereomix to work with hypercam when I make tutorials for my youtube etc to pick up system sounds which I could previously do on Vista. So I thought ok, and reinstalled the realtek drivers online for vista. Stereo mix still never appeared. I tried other drivers people suggested and looked at other people having the same issues. I seem to be the only one it won't install properly for. Currently my only recording devices are listed as

Microphone
2- high definition audio device
Not plugged in

Microphone
2- high definition audio device
Not plugged in

Disabled devices are all showing. I have one professional usb mic which isn't plugged in, and nothing else. But both are named the same and greyed out. I've tried enabling them, but no stereo mix appears and they don't show up as recording options in Hypercam so they are essentially useless. As for playback sounds, It shows

Speakers (default sound device)
2-High definition audio device
Working

Digital output device (SPDIF)
2-High definition audio device
Working

Default output device (HDMI)
High definition audio device
Working

That's all that comes up, again with hidden devices shown. I had Line in and stereo mix before I reinstalled windows vista, but neither of these are here this time around.

I'm honestly losing all hope at the moment, the realtek doesn't seem to have installed at all. Where do I go from here? Has the reinstall lost my chances of getting stereo mix back on vista??