Good news: it worked. Not sure what I was doing wrong the first time I tried it, but pressing Fn-F7 finally worked. Seems to be a fully functional machine except for the screen.



By the way, elsewhere I was told that another way of forcing video output to the external port is by unplugging the cable that connects laptop's screen to the motherboard. Did not have a chance to try it so not sure whether that's actually true. But might give it a try next time.