Other who had the same issue solve it by doing this:
1. Either connect your Mic to appropriate jack (don't mismatch with output jack for earphones etc.), or if you have integrated one, go to 2.
2. In Vista (shall be similar or same in 7, XP)
go to Start->control pannels->manage audio devices (or sounds...)->recording
3. Either there is listed something or there's nothing. In both cases: right click in the empty area, from context menu make sure that both options are ticked (show disabled, switched off devices - or something like that). Now you shall have listed all devices recognized as Mics.
a) There is still nothing listed, i.e. you don't have your Mix properly installed and/or recognized. If that's an integrated one, try to get drivers or consider reinstalling drivers. For external one, try to use another if you can or test it elsewhere.
b) There is exactly one device - just go to 4.
c) There are more than one device - I would recommend you to try to pick one you believe is correct in your case (e.g. don't pick up external when you're trying to run integrated and so on) and disable all others. You disable them by right clicking on each and then choose something like Disable from context menu. You shall be able to turn them back on if you follow step 3.
If you have no idea which one is supposed to be correct, you may try to pick up just one after another.
4. Do you still have no Mic listed after 3.? Then what the hell you're still doing here - you're screwed already!
Otherwise, you might be the lucky one. Or screwed too. You're gonna find out that soon. :-)
From the list that shall now contain just one item - one Mic - (you didn't close that window, did you) right click on it and from context menu select Properties. New wnd shall appear, with 2nd tab from left being Levels. Make sure that:
a) There is nonzero value for Volume bar.
b) On the icon next to Volume bar the sound isn't marked as muted. Click on it once if it is.
c) As for the Amplyfier - it's up to you, I recommend you to set it to 0.0dB or maybe 10.0 dB with Volume on 100. Don't know if you can somehow damage you're hw if you set it too high, shall not, but who knows (read botom line).
5. Close config window with Levels tab (OK button). In the list make sure that device is described as Active/Enabled/Whatever like that, and maybe select the only item in Mic list and click button Make this device default (or similar to that). Just for sure. You can now close all the config windows. I recommend clicking on OK buttons instead of Storno/Cancel, unless you love doing it all over again.
6. You shall now be ready to test recording performance of your Mic if any. I reccommend using program that can be launched from Start->Accessories->Sound Recorder
(or something like that). It shall keep default Windows settings which we've just configured. Try to record something with it. If an error message stating that you've got no Mic configured appears, go to 9a.
Otherwise you shall be able to start recording, so scream like lunatic during recording phase, since you'd like to check that Mic is at least able to catch anything. Stop recording, save file.
7. Open recorded file in Windows Media Player. It is just plain audio, so I recommend you to change Visualization to Oscilator (Right click, somewhere in context menu shall be Oscilator item, click on it). Start playback of file.
a) You've got some sound - you hear it or oscilator, huh, oscilates (changes from straight line). Idealy both at the same time. Go to 8.
b) Oscilator stays straight line all the time and you hear nothing - go back to Mic config (step 2, step 4) and on Levels tab for your Mic check that you've got all your settings as you left them - especially check the mute/unmute icon if it didin't switched back to muted. If something has changed in here, go to 9b.
8. Sounds like you've got you're Mic working, congrats! If you find it useful for others, post here what you did and possible problems you had to solve and you did it (especially if you did it in XP or 7 and there are any changes).
However you're not done yet. I recommend you to re-check the Levels tab (step 4) and take especially attention to Amplify level. You may wanna turn that bar down on behalf of Volume slider. Or it's up to you. Of course any changes to Mic. Input Volume shall be made here too (in 3rd party applications you would find another slider for Mic.). That's all.
9. Problems section.
a) Sound recorder states that you're Mic is not configured abusing an error message for this Purpose.
You may wanna re-check your Mic config (especially if you have selected any - shall be one - Mic as active and default one in config window) AND check 9b.
b) May sound strange, or may not, but try unmute your Mic if it is muted and before closing the window, mute all Output devices (speakers...). Of course if Volume or Amplify levels changed, change those too (however - may be that you're OS leveled down the Amplify value because it recognized it as Mic incompatible - maybe, quite possibly shall not happen). Close all config windows and try from 6. Don't forget to unmute your output sound device after recording during playing in WMP or just check the Oscillator line.
c) Unknown **** happened. Well, it happens, we all know.
If you were able to finally find solution to your problem, please post here. If you weren't just post here your problem.
BOTTOM LINE: I'm not responsible for any havoc or damage to yours or any others computer, life or anything else that would be caused by following this guide. Quite possibly not any new information appeared here in comparison with previous posts, but I guess that this guide is quite step-by-step, so you may find it comfortable to use this. Or may not. It's up to you. I hope that this makes some sense and for parts that would not make sense to you, I guess that you would be able to guess what was it about. Typo mistakes may be found too.
Good Luck. :-)