Generally after macOS release of new version of Operating system there must be an error with every macOS update released. Mac users face many errors during installation of Mac operating system and face trouble due to less amount of space in the drive or due to corrupted system files and for every upgrade user must boot in recovery mode to install OS.
If you are not able to reinstall macOS Sierra without loosing data you can read to know How to reinstall macOS Sierra without loosing data. If not able to upgrade Mas OS to latest version then follow below mentioned methods to fix Mac OS X could not be installed on your computer.
METHOD1: BACKUP OPERATING SYSTEM AND CLEAN JUNK
Step1: Open timing Machine by searching from finder.
Step2: Open hard drive and delete duplicate files, move big files to external drive.
Step3: Search for left over files, temporary files, unused files no more required and delete them.
Step4:Run First aid to check for corrupted files and restart no completion.
METHOD2: FLASHING macOS
Step1: Restart Mac with copy of flash drive containing full version of Operating system.
Step2: If not able to complete due to corrupted files it will reboot system in recovery mode or if in stuck a boot loop press command + R to enter recovery.
Step3: In recovery mode if you are automatically connected move to step4 if not try to connect to internet and keep your Wi-Fi password handy.
Step4: Follow on screen commands and make sure your system date and time zone must be correct.
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