How do you fix the setting on your inspiron whenthe lights dim when you plug it in?

I'll assume you have Windows 7. If not, then instructions should be similar, if not exact.

click the battery icon at bottom right of screen.

click "more power options"

click "change plan settings" of the current one you're using

and you can manipulate the options from here.

the fourth option shows how much brightness the screen should be when you plug in or when you remove the charger.