I have a Toshiba Satellite Pro C50-A-1E2 laptop (p/n PSCG7E-02C041EN) which has developed a fault on the screen (4 second video here).
An external monitor on the HDMI port works fine. When it first happened, a little percussive maintenance fixed it for a week or two so I'm sure it's a hardware problem but I don't know whether it's the screen, the motherboard or the cable between them. It has only the internal Intel HD 4000 graphics. Could anyone offer a definitive answer?
I was going to ask on Toshiba's forum's but it looks like the answer to all hardware problems there is "return it to a Toshiba Authorized Service center".