Powerbook G4 straining and turning off

My 2004 17" Powerbook G4 (with an almost-dead battery that only barely works and always needs to be plugged in) is making strange straining noises coming from below the screen when in use (when pressing keys, or using track pad). There's a burning smell though the computer is not hot, and after long use, the screen gets wavy/goes out. I tried taking out the battery and just leaving it plugged into the wall, but then it wouldn't turn on.

Any ideas?