A broken LCD will have dark crack lines if you hold it up to the sun (that would involve removing the LCD and separating it from the backlight (not a good idea)) It could be a damaged PCB on the LCD side as well in which case a new LCD assembly would be needed. The problem is, there are a bunch of possibilities, and none of them besides the cable are readily fixed.
There is also a chance that you could get a new monitor assembly, but those can often run in the $50+ range, which is likely not worth the trouble.
As for the external monitor not working, that sort of makes me think it is an internal video adapter board or section of the motherboard with the problem, as that would explain how you either have video or you do not.
I...