How to reinstall macOS High Sierra?

Hi Manoranjan75,

Given your situation, you have a couple of options. You could restart the High Sierra installation, or revert back to Sierra if you made a Time Machine backup before this incident.

To restart the High Sierra installation

1. Hold down Option-Command-R as you turn on or restart your Mac. Release the keys when a spinning globe appears. This will boot the latest version of Recovery Mode over the Internet, which will offer to install macOS High Sierra.
2. When the main Utilities window appears, select Disk Utility and continue.
3. Select your startup volume and click First Aid. If the First Aid button is greyed out, click the Mount button and enter your login password when prompted. Then, click First Aid.
4. If First Aid reports successful, quit Disk Utility and select Reinstall macOS. (or Install macOS)
5. Progress through the installer and wait for it to download a fresh copy of macOS High Sierra. Once this is done, your Mac will restart and start the installation over again. No data will be lost by doing this.

To restore from a prior Time Machine backup

1. Hold down Command-R as you turn on or restart your Mac. Release the keys when the Apple logo appears. This will boot Recovery Mode locally.
2. When the main Utilities window appears, select Restore from Time Machine. You'll be guided through the restoration process. If desired, run First Aid on your startup disk before beginning the restoration.

Hi,

Probably your drive messing up, so need to reformat which means you lost your data.

Booting in Recovery mode then reformat with Disk Utility, then reinstall macOS.

About macOS Recovery - Apple Support