Can't open my mac after installing windows using bootcamp My macbook pro isn't working well after I installed windows 8.1 using bootcamp. It displays the blue screen, and get an error. Now there is only Windows option in startup, and it says that your PC need to repair. 

I can't open either Windows, or Mac, and the big thing is there's no mac option on startup.
Boot to recovery mode and then choose the Mac startup disk might be the fastest way to determine if the Mac is still bootable.

Apple documents this and the other ways to switch back and forth at:


https://support.apple.com/en-us/HT204417


If you've meticulously done all the steps, you might ask a second follow on question with more details about what the situation is.