Are you having trouble getting your Mac to start up? If your Mac computer with an Intel processor is displaying a white or blue screen, a question mark, or is not booting at all, there could be a problem with the firmware, startup items, or software. It's possible that something went wrong during an OS X or MacOS update. This can lead to a damaged system that won't boot, or one that boots but is unstable and crashes. To begin troubleshooting, first check that the wall outlet is turned on and secure.
Then try a power cycle to completely eliminate all traces of energy from your Mac and restart it from scratch. If you don't hear the startup sound, fan noise, or any visual elements on the screen, it means your Mac won't turn on at all. If you're getting to the point where it refuses to boot, try restarting your Mac and holding down the Option + Command + P +R keys until you hear the second ring. This will reset the NVRAM and PRAM in MacOS Mojave.
Alternatively, hold down the Command+R keys until you hear the start bell or see the Apple logo. This method can help if your primary user account has problems when starting up or using the Mac. If your Mac computer with an Intel processor shows a blinking question mark when it boots up, this indicates that the system software can't be located. To reinstall MacOS, make sure your Mac is connected to the Internet and boot into recovery mode by restarting your Mac while holding down the Command and R keys until you hear the start bell.
These are some of the methods you can use to troubleshoot startup issues with your Mac. If you're still having problems after trying these steps, it may be necessary to repair the boot drive or diagnose the problem in more detail.