How to reset a salvaged Mac Pro which has previously been managed? My buddy hauls junk and the Art Institute of Philadelphia closed down and had him remove a bunch of old iMac/Mac Pro’s from the college. 

I now have my hands on a Mac Pro 2010 tower and Cinema Display or whatever. 

This computer has deep freeze, and every time I turn it on it auto logs in to the “student” account which has a password. The other accounts (admin/cs-admin) are locked up too. 

I’ve tried recovery mode, for some reason it won’t boot in recovery. In single user the commands to add or delete user accounts won’t work either, I get errors every time. 

Worth pointing out is the GPU (Radeon 5770) wont work on Mojave so I need to run High Sierra. 
I just installed high Sierra on an external hdd as well. 

Is there any way to bypass the existing hard drive in order to just wipe the whole thing clean and have a out of the box copy of Mac OS X?

Been trying to figure this out all night so any help is appreciated
That machine is too old to boot to internet recovery. You will need to bring another OS - perhaps installed on an external hard drive and hold the option key when you boot. A DVD works as well, you will likely be able to copy files off but will need some skills to bypass deep freeze, that’s designed to keep out highly motivated teens with hours of free time. 

The easy path is to erase the drive and install the OS you please. 


https://support.apple.com/en-us/HT201255


The help above shows the various startup keys and links to other articles on reinstalling. 

Eventually, your path will land at the bottom of this article covering other ways to reinstall if you can’t get past deep freeze. 


https://support.apple.com/en-us/HT204904


Since you have an external, just use disk utility to wipe and then clone it or rerun the installer once you have backed up any files you want.