I have a brand new Gateway GT5694 desktop computer, using Windows Home
Premium (x64). I have a set of Altec Lansing speakers which I've plugged
into it, which worked very well with my previous XP computer. There's an
echo in the audio output that's so bad that speech is barely intelligible.
There's also mild distortion in music. Headsets work fine when I switch to
those; no echo at all. Speakers consist of a small left and small right
speaker, and a sub-woofer. They're powered speakers. The speakers' green
input plug (only one) is plugged into the green, speaker output on the
computer. I've tried all the other 3.5mm outputs, and none of the other
outputs work at all insofar as producing sound. I've tried different
settings in the Control Panel (Manage Audio Devices). Does anyone have any
ideas as to what's causing the echo and how I might fix it?

Thanks!