Yes, I fixed it.
After three months, I heard some noise from behind the laptop.
Oh my.... again?
When I wiggled the connector, it sometimes worked.
As before, it finally stopped working.
I had to open and re-solder the power plug.
That happened .... at least 5 times.
Finally I was fed up with the re-soldering.
The problem is coming from two facts.
1) DC power jack is fixed on the mother board not to the exoskeleton of the laptop. Therefore any shock to the power connector is directly transduced to the soldering between the power jack and the mother board.
2) Joint between the power jack and mother board is highly oxidized and always ends up in un-clean solder. Even a small shock on the power jack makes the soldering connection cold.
For the solution
Fix the DC power jack on the outer case not on the mother board so that the soldering at the mother board is isolated from any external shock.
How can I do it?
Step 1: Modem Jack Removal
It's usually unused in modern computing unless you have dial-up.
In order to reach the modem port, you have to follow this Instructable to the step 9 and remove the modem jack.
Step 2: Power Jack Preparation
Then the jack is soldered to the electric cords.
The power cord is from an adapter for my old telephone. It could be any power cord.
However, it should be thick enough to support the electric current needed for laptop.
Therefore the use of those audio cable, phone cable etc. are not recommended.
Step 3: Fix it on
You can put the PC board back on.
Step 4: Re-assemble
Now you can see the empty hole which was occupied with power jack before.
And the modem port now occupied with power jack.