Can you attach an external monitor to these to laptops?
If so.. do it.. see if the problem is repeated to the external monitors. If the problem is, then you could have a bad video driver (not that likely) a virus that plays with the screen(also not that likely) or you could have hardware failure (most likely).
If the problem does not show up on the external monitor, then the problem is the LCD itself, or its base parts, the driver, the back light, etc. If the problem does show on an attached monitor, then it is more likely the video memory or connections from the video output going to the LCD driver and the external connector are bad ... usually traces on the mainboard inside the laptop. Its possible that stress, heat, and any twisting of the laptop may have loosened connectors or caused enough problems with board traces if the boards are weak or have had harsh twists, falls etc..
If you're lucky they will be under warranty.. if not.. its often cheaper to just buy new than seek repair. Additionally if you do replace them, remember its just the "built in" screen that could be bad, and you could use these laptops for other things, attached to a monitor, or as one friend I know does, uses them as linux machines (servers, remote command line workstations)... they work fairly well, and no on screen session is generally needed once they are set-up.
