Software Update Loads but doesn't run

I have a new MacBook Air. Tried to migrate from an older MacBook Pro. System says I need to upgrade to latest High Sierra version on the Air to match the pro. Software update downloads, and machine restarts with screen showing update in progress. The progress bar shows about 1 16th of an inch and doesn't move. After three hours, I powered down the machine. Tried it again with the same result. Downloaded full High Sierra from App Store. Goes through the first couple of steps of installation, restarts and then stalls. Thoughts? Suggestions? I'm all ears.