My guess is something you copied from your MBA isn't compatible with the new machine. It's also possible something glitched in the process. BTW, what is a "buffer icon?" Press and hold down the Power button until the computer shuts down. Wait 30 seconds, then restart. If the problem persists, then do the shutdown, wait, and restart again but follow these steps:
Reinstall El Capitan or Later Without Erasing Drive
Please be sure you back up, if possible.
- Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
- Select Disk Utility and click on the Continue button.
- Select the indented (usually, Macintosh HD) volume entry from the side list.
- Click on the First Aid button in Disk Utility's toolbar. Wait until the Done button activates, then click on it.
- Quit Disk Utility and return to the Utility Menu.
- Select Install OS X and click on the Continue button.