That's an old thread, but it appears I'm still subscribed to it.
What I found after that, is that you need to install the ALSA sound module for this onboard sound to work properly. You can search threads for how to do this. I've done it under Debian now, having run from the bloated RedHat distro I was using at the time of these old posts.
I don't know what is the cause of your problem now, but I hope you haven't fried the southbridge chip, or whatever runs the onboard sound. Before running anything else out of the mic jack, I'd be certain to get some expert opinion. Maybe even have your motherboard checked by someone reputable. Where do you live? If in the U.S., I seriously doubt if such a person exists in a chain type computer store.
Maybe you can post a new thread of your own and someone who really knows what they're doing will respond. Don't just blindly follow anyone's advice, as we're all free to give it in LQ, and sometimes it may be just an educated guess (the reason I don't post the way I installed ALSA in Debian for you to do in Mandrake).
Hope you get it solved, and there's no damage to your board!
Maybe it would be a good idea to post in the Distribution forum and get some direction for installing ALSA under Mandrake. It's obvious you made it here by searching the forums, so I don't think you'd mind waiting a little longer. The distro forum probably gets less hits, but more specific posts and less of us newbies, I'd think.
Aussie and bjb123 have posted the correct answer. Look for bjb123's link which starts:
You need to get the alsa drivers from
www.alsa-project.org, then:
and follow that advice. Also, Aussie is a moderator, and knows his stuff, and read whatever he says about it - I'm certain that will work.