Today an odd problem came up with an IBM T43p laptop. The screen randomly goes blank. Not entirely blank, but so dim that you can't really see anything. If I hit Fn-F7 (the key to switch to an external monitor) it will come back for a minute or two. No external monitor is connected, by the way. If I do connect an external monitor it will stay on with no problem. So is this a problem with the screen, or could it be something else?