Computer stuck on macOS installer

Boot to the Recovery Volume (command - R on a restart). Run Disk Utility and select First Aid. Then re-install the OS.

OS X Recovery

OS X Recovery (2)

If that gets you a working computer, you can try the installation again, perhaps using another admin user account.

Please note the absence of an included image.

To Post A Screen Shot

1. Press Command-Shift-4 which will change the cursor to crosshairs.
2. Hold down the mouse button and use the crosshairs to select the part of the screen you wish to capture.
3. Release the mouse button and the image will be saved to your Desktop.
4. Drag the pic into your open forum editor. If that fails then go to the following steps.
5. Click on the Camera icon in the toolbar of the forum message editor.
6. Drag the image onto the Choose File button and click on the Insert button.

Press and hold down the Power button until the computer shuts down. Wait 30 seconds then restart the computer. This may get the installer to continue assuming there is no other problem.

What to do when a macOS update goes wrong

Generic troubleshooting- how to fix something that doesn’t work

Please provide complete information about your model. To find the model identifier open System Profiler in the Utilities' folder. It's displayed in the panel on the right. You may also find the complete model information by selecting About This Mac from the Apple menu.