Go to System Settings, Sound and then to the Recording tab. If your microphone is listed there, double-click. Set the slider under "Level" to 100, then it should actually work. My Rode NT-USB is so sensitive that you could almost use it as a directional microphone.

When was the last time you did a "spring clean" of the registry, e.g. with CCleaner? I could well imagine that this would be useful. This way, my box also recognised the microphone again, after it had always said that I should plug it in (although it was plugged in).

Many thanks for the tips! It seems to be a specific problem for me, as I had set the system setting and controller mentioned (but it always resets) and also activated the microphone in the respective software. How close does it have to be to the mouth for it to be clear? Is 20cm too far? Many thanks