My new MacBook Air is stuck on the Apple Logo and won't start.

Hello hilaryfrommarkham,

Welcome to Apple Support Communities. 

Please try the steps as listed here: If your Mac starts up to an Apple logo or progress bar - Apple Support

1. Press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off. (Every Mac has a power button. On notebook computers that have Touch ID, press and hold Touch ID.)
2. Turn your Mac back on. If the issue persists, press and hold the power button until your Mac turns off. Then unplug all accessories from your Mac, including printers, drives, USB hubs, and other nonessential devices. You could have an issue with one or more of those devices or their cables. 
3. Turn your Mac back on. If the issue persists, once again press and hold the power button until your Mac turns off. Then follow the steps in this article: How to repair a Mac disk with Disk Utility. It explains how to start up from macOS Recovery so that you can use Disk Utility.

• If Disk Utility found no errors, reinstall macOS.
• If Disk Utility found errors and repaired them, restart your Mac. If the issue returns after restarting, reinstall macOS.

These steps will resolve concerns similar to yours.

Let us know if you have further questions.

Take care.

When using Migration Assistant, only selected groups of files and/or apps are transferred, along with your preferences. The already installed OS in the new computer will not have been affected. I suspect that something may have been done in the setup process to damage the OS. I would follow the steps suggested above to resolve the problem.