it's probably just a routing issue. start at the winamp output plugin configuration and work your way outward till eventually the DA process.
make sure you're routing with VAC properly for whatever you have to do, and if you need an output from VAC and you're not using any application that doesn't do that in realtime (or are only using recording app) then remember to open a VAC Audio Repeater before recording so you can hear the output in whatever DA you need.

also make sure to give a nice check into the soundcard driver's control panel and/or microsoft sndvol32 (aka volume control)