A prohibitory symbol, which looks like a circle with a line or slash through it, means that your startup disk contains a Mac operating system, but it's not a version or build of macOS that your Mac can use.

1. Boom Audio Mac

Explore the world of Mac. Check out MacBook Pro, MacBook Air, iMac, Mac mini, and more. Visit the Apple site to learn, buy, and get support. With a classic arcade feel, the game is fully 2D, offering smooth sprite-based animations, eight soundtracks, 80 levels of bomb-exploding action, and a final 'Boss' character that will challenge.

Boom Audio Mac

1. Press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off.
2. Turn on your Mac and immediately press and hold both Command (⌘) and R to start up from macOS Recovery.
3. While in macOS Recovery, use Disk Utility to repair your startup disk.
4. If Disk Utility found no errors or repaired all errors, reinstall macOS.
5. If you still need help, please contact Apple Support.