Presario 2100 and dimming screen

hello,

i have a presario 2100 that the screen continually dims and undims. i know this is from the power continually switching between AC and battery. but the weird thing is that this happens even when the battery is pulled out. does this sound like a physical hardware problem and/or is there anything i can do to stop this?

thanks.
-- neo TheCat

it is ~5 years old. i think....