I too had the same problem and posted my query on 4th September 2009 (yesterday) after I had tried a number of other things including replacing the battery.
I received a prompt response from joegoldman only a few minutes after posting the query. My sincere thanks to this person's excellent instructions I managed to dismantle my laptop and fix it on the same day.
It was indeed the dry joints causing the problem. I also had to apply some solder at the back of the power socket to stop the slight wobble of the pin on the power socket to prevent it from happening again. I also had to remove the hard drive and its base which was screwed on to the back panel through the mother board.
I suggest you too try out Joe Goldman's solution , which I am pasting here for your reference. Good luck. If I can be of any further help to you please let me know:
"First thing is to remove the top bezel. This is the piece of plastic between the keyboard
and the display. Since you have removed all the bottom screws, you should be able to pop the bezel off by inserting the tip of a small flathead screwdriver under one of the plastic hinge covers. Check the back of the hinge covers for screws and remove any you see first. Once the bezel is off, remove the screws securing the keyboard and remove the keyboard. Be careful with the keyboard ribbon cable and the connector for it, they are fragile. Flip it over and remove any bottom panels. Disconnect the wireless antenna cables from the wireless card
(usually black and white). Flip it over again. Snake the wireless antenna cables up through to the top and disconnect the other thicker cable (video and power) from the mainboard. Now you need to remove the display. After the display is off, remove the optical (dvd) drive. Remove any case screws you see from under where the keyboard was. You should be able to get it apart now. Be VERY mindful of connector wires/ribbons as you take it apart.
When soldering the joints (do em all on the power jack) be careful not to heat up the area too much as there are often very sensitive fuses close to the power jack. Do the joints quickly and do not use an excessive amount of solder. After you solder it, dry-fit the laptop back together and test it. If it's good, lay a small bead of hot glue around the base of the dc power jack to reinforce it."