Compaq presario Power mixup

I'm using a presario R4000. The ac power doesn't seem to be working properly as it takes a long tome to charge the battery. The strange part, though, is that the screen is dull when on ac, and bright when on battery power, as opposed to the other way round.
Also the ac power light only comes on when it's plugged out and running off the battery.
Is this the start of a serious problem, and if so do I need a new adapter or is it the motherboard connection?

getting nervous, any information welcome.

Screen brightness can be set up differently for DC power and battery power, you can set your personal preference by pressing FN key together with the brightness up/down keys. Do the same thing for when laptop is pluged on DC and for running on battery.
The problem you describing with the power adapter it might relate to the dry jointed mainboard power plug OR mainboard fault.

It's a farily inexpensive fix - you only need to find the connector (which may be difficult). If you can't find just the connector, you'll need to get a motherboard that uses that connector (damaged or not...just as long as that motherboards connector works)

In terms of hassle, it's not too bad either. You will be required to dissassemble your machine down to the motherboard, then desolder the connector present and solder on the new connector.