If you mean High Sierra macOS 10.13, make sure your Mac meets the requiements > macOS High Sierra - Technical Specifications
Otherwise, see if a Safe Mode boot gets your Mac back in action.
Shut your Mac down. If necessary, hold down the power button until the screen goes black.
Wait at least ten seconds then follow the instructions below.
To start up in safe mode:
- Start or restart your Mac, then immediately press and hold the Shift key. The white Apple logo appears on your display. If you don't see the Apple logo, learn what to do.
- Release the Shift key when you see the login window. If your startup disk is encrypted with FileVault, you might be asked to log in twice: once to unlock the startup disk, and again to log in to the Finder.
To leave safe mode, restart your Mac without pressing any keys during startup.