Car won't start just clicks once

I have a 2002 Buick regal ls, when I try to
start it, it just clicks once, the lights on
dashboard go off and headlights too, as
soon as I let go everything comes back on,
headlights are bright again, I thought it was
the starter and battery, took both off and
took it to autozone they said starter is good
and I took battery and put it on another car
and it starts right up, I though Mabey it was
corroded so I bought a wire brush and
cleaned both, still just clicks once, help me
please.