Mic stops working

I've had some problems with my microphone lately; at first friends said my microphone made a lot of crackling noises when I spoke. I was able to fix this by changing to 16bit 44k Hz format. However this doesn't work properly anymore, as when I do any changes my microphone will stop working entirely. Sometimes, but usually, it will register noises on the green bar @ Recording devices, but makes no sound in my headphones ("Listen to this unit" enabled). I do no changes to the cables in any way.

I got a Creative Audigy 4 pro sound card, W7 64bit, sound card drivers updated. Any ideas to what's wrong and how I can fix it?

Just turned on the pc and microhpone is dead.

@ Dwarf: nothing, basically. I have seen it register noise on the green bar, but not all the time.

@ Maceman: Yes, it is connected via the Audigy 4 pro external unit (Line in 1/mic) with a mini jack. As I have two of the same headset, I tried to switch but there was no difference; still didn't work.

However, this time I have one extra report: although Line-in 1/mic is standard unit, Windows said that Line-in 2 was ready for use, and the green bar was on this unit rather than line-in1 where it should be. As I wrote this, my microphone suddenly worked again, but with the annoying waves of echoing crackles when I speak.

It's almost as if I open Sound setting once and try the different options, nothing changes. But if I close settings, go for a quick walk around the house and open Sound settings again, my changes will work (for removing the crackles).

I've disabled all unused in and outputs now, will see if it makes a difference the next few days.

Yes, I can change volume control on both my headset and external Audigy 4 unit (if that is what you asked?), and have turned them both up to high volume - or otherwise my sound is simply too low for others to hear. I can barely even hear myself talk right now, and that's with sound level at 100 in Windows.

I change settings for this every single time I turn on my PC now. Why is it always bugged? Why does my PC revert back to crackling noises after fixing them the day before?