Somebody with a similar problem on a different forum:
"So here are the steps that worked for MY laptop:
Having your laptop running and plugged in, let the battery die at which time the screen will turn off.
Press the On/Off button until the laptop powers completely OFF. Be sure to leave it plugged in.
Wait a few minutes. You will notice that an orange light will turn on where the adaptor plugs in to the laptop.
Once this happens, wait a couple more minutes.
Finally, power up your laptop. You will notice that the power meter on the task bar will now read "Plugged In. Charging". Your laptop is now charging while ON!
I really hope this works for you. If it does and I saved you a headache and a few bucks, do something...