I'm guessing you've got a Presario (or equivalent) laptop from the past 2 or so years. Yeah, I'm on my third PS right now (second from eBay). I don't know why, but whoever designed this particular PS needs to be shot. There's too much strain on the connector at the computer port, which is what causes the whole thing to fail.
Funny thing is, my wife's iBook G4 has the same issue. If only we had waited for the MagSafe models to come out and not worry about the poor design for her PS, as well.