I havent posted here in while, but this one I may help out on.
My wife's laptop was doing the same thing (not charging). However, every once in a while, if you played with the end of the plug, it would start to charge.
This led me to think it was the female part of the laptop that you plug the adapter into (the thing with the little pin on the inside of it). I know on some bigger models of laptops, that end piece comes free from the board.
Using the guide to install the 2GB of memory (actually I used the service manual from Dell - but they are pretty much the same), I worked my way to the round plug. TIP! - When removing the keyboard, use a small screwdriver and push up though the hols to pop up the keyboard. You'll see what I mean)
The Female end of the adapter has two leads that come off of it. THey then plug onto the main board via a little white clip. The wires are soldered to the female end of the plug and then taped with a little strip of black tape.
I was able to pull one of the wires free from the round plug with ease (i think it was the black wire). This explained why, if you played with the plug it would sometimes connect.
Using a razor I gently removed some of the shielding from the end of the wire and then soldered it back to the end of the plug (I call it a plug - but it's the female adapter - the thing with the pin in the middle of it).
Its very easy to see where you need to solder it to.
I replaced the strip of black tape and since then it's been stable.
I know it sounds confusing, but the hardest part is taking the laptop apart - and if you take your time and label the screws you remove, its not hard at all.
I hope it helps. I say you have a look to see if your wires came free like mine did. If they did, then since you are already there throw a 2gb chip in there too.