550P Laptop not charging the battery and won't work just on charger.

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Hi everybody, I wonder if anybody can help, I'm getting desperate!  I have a 550p i7 laptop.  If I plug it in with no battery or a flat battery it wont fire up (but the red battery light is on).  If I put a charged battery in it works fine.  It says that it is plugged in and the battery icon moves up and down as if it is charging, but it isn't!  The power slowly drops until the battery is dead (even though it is plugged in).  I have replaced the battery and the charger. I have reinstalled the battery drivers.  I have also replaced the charger port and the charging controller IC chip.  However,  it is still the same! I am now at a loss and I am reluctant to spend much more on this laptop.  Any advice would be welcome.

TIA 

Dave