Can't open my mac after installing windows using bootcamp
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.