|I have exactly the same problem.|
1. My screen is completely broken (can't see a thing) and,
2. I think there's a problem with start-up (I can't log into Windows to switch to external monitor)
So, I am also looking for answers on how to switch to external display during start-up also.
I can access BIOS by repeatedly pressing F8 on start-up but I can't see what I'm doing to try to fix the problem.
The problem here is that the fn + F7 function only works when logged in to Windows.
According to my research, the only option is to fix the broken screen OR try to fix the laptop with system restore on BIOS without seeing anything i.e. blind!