The only reason for why the sound cuts out (goes back to zero) at the start of each new track is if the volume slider in Winamp's main window is set to zero. Adjusting the Wave slider in Windows Vol Control won't have any affect, because if Winamp's volume is zeroed then it will still reset itself to zero again when the next track begins... regardless of Alt Setting mode etc.
There's a screenshot in this thread to help you even more:
If the problem persists, then I'm not sure what's causing it...
but then again, you didn't provide full sys specs.
I take it you've made sure gen_nomad.dll
Have you installed any other 3rd-party plugins? If so, which?
I doubt if uninstalling a vis plugin could cause this kind of problem.
It's more likely to be one of the other types (dsp, input, output, general).
Are you sure you read/tried EVERYTHING previously mentioned?
What type of files are affected?
MP3, WAV, AudioCD, MIDI, WMA, other, only one of these, all of these?
Basic Uninstall -> Reinstall procedure: