Battery won't charge when Laptop is running !

My Inspion 1100 won't charge the battery if the laptop is switched on. The battery charges only when the laptop is switched off and the adapter is on. If, when I switch on the laptop, the battery is say 60 % charged, it remains so for as long as I run the laptop, even though the power adaptor is on. The battery does not drain away, but neither does it charge to more than 60 %. I have to switch the laptop off and only then does the battery continue charging. Please help.