|"I have been told that it is the bois, not recognising the Ac adapter, that cause this problem..."|
That's Bullxxxx !
Some people think every problem can be cured by updating the bios version !
Flashing the bios is the riskiest thing you can do with a computer !
You are taking a big risk when you flash your bios - if the flash fails, and/or the flash chip physically fails while flashing (this is COMMON - these cheap flash chips can only be flashed an unpredictable small number of times), you will have a mboard that will not boot.
If the flash fails, but the flash chip is physically okay, you can follow a specific Recovery procedure, according to the brand of your bios.
If the flash chip physically fails you will have a dead mboard until that is fixed, and you need to obtain a new flash chip, already flashed.
Most if not all laptops have a soldered-into-the-mboard bios flash chip, not a flash chip in a socket that can be removed. In that case, the flash chip can only be replaced by an expert with the proper de-soldering tools and usually you must ship the mboard to them and have it shipped back - that can cost more than you buying a good used mboard for your model.
IT MAKES NO SENSE AT ALL to update your bios if it was previously charging the main battery correctly !!
The most likely things are....
You may have the problem mentioned in the last part of response 3 - Dell usually has a Service manual available on the their web site for your model or model series that tells you how to take apart your laptop properly - or you may have a problem with the jack the AC adapter plugs into that needs to be fixed..