Some updates could not be installed because "x" interrupted restart. To continue, quit "x."

I think the problem might be that the new operating system which was installed may have been downloaded via Wi-Fi and because Wi-Fi is often too slow for those very large files, it got corrupted during the download. I suggest reinstalling the OS. If you can, download the file via a wired Ethernet connection. If that is not possible, you may have to do multiple downloads to get a clean one that will properly install. You can restart the computer in the Recovery Mode to do a new download. Press the Command + R keys on startup. I hope that helps.

Hold the Power Button until the computer turns OFF

Let is sit that way for about 30 seconds.

1 - Restart in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal.

2 - Safe Mode will also eliminate Third Party Software, extensions and drivers from loading. It will only load the Minimum amount of Core Apple Processes to allow the the computer to function at a reduced Level of Performance 

3 - Does the issue present in this mode ?

4 - Sometimes a Safe Boot followed by a Normal Boot will just put things right.