Announcement: Upgrade to macOS Mojave
With features like Dark Mode, Stacks, and four new built-in apps, macOS Mojave helps you get more out of every click. Find out how to upgrade to macOS Mojave > https://support.apple.com/macos/mojave
Question: Whenever I start up my Mac there is a screen with a circle with a slash through it. I have tried to download Os Sierra but it says that my computers validity needs to be checked with Apple.What do I do?