I find the input “the input volume slider” will be moved to right most point (maximum scale) and it will be gray out (I cound not adjust or move the slider to reduce input volume. Because maximum input volume, the sound pictures generated will be much loud noises, which is impossible to remove its noises under audacity v2.0. Any way Audacity v2.0 could be properly installed under Microsoft Window 2000 professional?
See http://manual.audacityteam.org/o/man/mixer_toolbar.html . If the input slider is greyed out, it simply does not control the system input slider at all. This is probably due to issues with the drivers of the sound device you are using.
We grey the slider out when it cannot control the system slider, because all Audacity could do if the slider was not greyed out in that case would be to make a distorted sound quieter, rather than turn the input down to stop it distorting.
So the answer is to turn down the input slider in Windows (Sounds and Audio Devices or similar).
Gale