If your iMac turns on but does not start up, go straight to step 2.

You should hear a small startup chime, perhaps some fan or drive noise and then some slight color change on the display. Check to see if your iMac is turning on and receiving power (hardware issue), but not starting up (software issue typically). Not starting up and not turning on are two different issues.

Simple enough but this is important to know.

For some users who installed the MacOS High Sierra update before the security patch was released a week later, this software update could have stuck your computer. Fixing this and getting your computer back up and running may be quick or take a while depending upon the problems that need to be addressed. When your trusty iMac does not turn on, it is easy to get panicked. A reboot of your Mac is another effective troubleshooting tool.Have you been alarmed to see your iMac suddenly stopped working after you installed a security update or used new software? Here’s what you can do. Updating to the latest software could patch bugs in your system. Check for updates in macOS by clicking the button in the menu bar and selecting About This Mac Software Update. Developers typically list the recommended operating software wherever you download the app from. Restarting your Mac essentially clears your macOS’s memory and starts it. Or press and hold the power button and, when a dialog box appears, click the Restart or press R. Hopefully, some data damage that can be fixed by restarting. Sometimes, if a USB disk won't boot, the cause is macOS issue. Create new test user account-1) Open System Preferences (Finder - Applications - System Preferences 2) Click Accounts 3) If the LOCK icon at bottom left is shown as being Locked, click the icon to unlock it. Thanks for the infoCustomer Please try the following as the next test: Create a new user account to test whether the problem follows the profile or not. Fix Mac won’t boot/start/turn on after macOS (11 Big Sur/10.15 Catalina) update Solution 1: Reset NVRAM or PRAM ON Mac Clear Cache of Mac RAM All Mac has these two types of memories that can able to store information like TimeZone, Karnal Task, Display Resolution, Startup-Disk Selection when it’s shutdown, and reuses while we turn on.

Mac won39t update software