What JorgeM said, although it can also be a simple matter of the LCD backlight being defective. If it is the backlight, sometimes you can see very dim images if you look at the display from an oblique angle with a light shining on it (sometimes better if the light is shining from the side).
The ribbon cable is under the keyboard! Have to remove keyboard gently and check cable. With the external monitor have you checked the boot log and event logs as these may give indication as to where the fault lies?
Yeah, i would just be very carefull opening up the laptop. I've done it back in the day a few times. On one occassion, I was lucky as it was just loose at the connector for some reason. On another occassion, I needed to order a new ribbon cable.
Keep in mind that the cable is just one possibility. Sounds like there may be other issues going on now that you mention that the touchpad isnt working either.