After Mac Sierra installation if Mac does not start its process, then it might be possible that the installation is not completed or some virus and malware has entered in the computer system. To fix this problem, you can call on toll-free number or visit http://applecustomerservice.us for Apple technical support for help. To resolve Mac problem, you need to follow some instructions but before attempting any step make sure that you have updated the OS to the latest release. Restart your Mac holding down command + option + P + R key to reset the NVRAM. Reset SMC (System Management Controller), shut the Mac down, unplug all cables wait a few minutes, and then connect them back and start up the Mac. Boot Mac in safe mode and make sure your Mac have 9GB of free space. Remove all the antivirus apps and all extensions. See if your problem is getting solved. For any other help on macOS Sierra installation visit http://mac-technical-support.com regarding Mac errors or issues, you can take help from Apple Mac technical support by calling Mac support phone number.