Powered off during new software installation. Locked out of MAC

Sure. Hook it up in Target Mode with another Mac. Drag and drop your User folder onto the other Mac. Now you can install a system from the master mac or, according to which Mac you have (you didn't say) you can do an internet install, install what you have on the master Mac (an installation download should be in your application folder), lastly and poorest choice (because you will not get the repair partition) clone the drive.

Tell Best Buy to stick it. Don't ever go back to them for help! Come here to see the real pros ;-)

Now with the $200 you just saved, go out and find a Vietnam vet that never got a thanks and buy him a decent lunch. I'll consider us even.

https://support.apple.com/en-us/HT201462

To steal a inspired quote from Gorge S. Patton Jr;

Best Buy Geeks "don't know don't know anything more about real Mac Repair than they do about ..........". Stay away from the corporate maggots, find an honest independent Mac Repairman by Googling and looking at his reputation. Google " your city & mac repair". Find a guy like this with a five star rating: https://www.thumbtack.com/tx/lubbock/com...

http://www.dailymotion.com/video/x156uvg...