I have a 2011 MBP which i bought with a faulty screen to use with an external monitor / TV which has all been fine until today. After seeing the upgrade to high sierra reminder everyday and ignoring it i thought i might as well give it a look and told it to go ahead without thinking about the display issue. After the initial restart all i get is a grey no entry sign on my external hdmi display and nothing i do will change that, I tried booting in safe mode by holding the shift key down but with the display open i don't get anything on the TV so no idea whats happening on the broken screen. I tried hitting shift on a wired keyboard after hitting the power button and quickly shutting the lid but again nothing. only if i hit the button and close the lid i get the TV on wight he grey no entry logo. So it looks like i killed my perfectly working laptop in no time. Any advise greatly appreciated.