My system was dual booted with CentOS 7 and Windows 8. After I reinstalled the latest Windows 10 Pro and removed windows 8, my system is only booting with Windows 10 as the Grub2 is not appearing at the boot time.I assume Grub2 is over written by Windows MBR. I might need to reinstall grub on my system. I don't have any clue on how to attempt this Grub2 installation as CentOS 7 is the latest version which is having many changes 
CentOS 7 grub option is missing after upgrading windows 8 to 10
linux;centos;windows;grub2;mbr
The solution was simple with the below steps.  Booted my system with CentOS 7 disk into a rescue mode.Now mount my root partition by running the chroot command as follows.  chroot /mnt/sysimage Then I installed MBR with the below command.  grub-install /dev/sda after installing the grub boot loader I rebooted the system, and it was up with any changes to the system.