System files accidentally locked

I have a strange problem.
My son was experimenting with system security and managed to lock up system files.
From what I can tell, he went into Properties on the top level C: drive. He went to Security, and individually selected each user besides Administrator (including SYSTEM). He picked Deny for all of them and Applied the changes.

If I try to get to the top level C: drive, I get C:\ Access is Denied. Most things do still run, but I'm not sure what problems it may be causing. One odd thing I've seen is that I can launch cmd from C:\windows\system32. If I try running cmd as Administrator, I get an error that the file does not exist.

Since the admin commands won't run, I don't know what to do next.

Any suggestions would be great. Thanks!

Do you have System Restore turned on? Give that a try. If you get Denied, try booting from a rescue disk or Windows 8 install media and try System Restore from there.

Maybe try to Refresh your system?

http://www.eightforums.com/tutorials/2293-refresh-windows-8-a.html

[EDIT]
If you know how to reverse what you son did, you can enable the built-in administrator account. I believe if you use that account, you will not get denied access. I think you will need option 2 to enable it. After it's enabled, and if System Restore is turned on, use that account to restore it. It's best to disable the account when you are finished.

http://www.eightforums.com/tutorial...rator-account-enable-disable-windows-8-a.html

If every solution fails, as a last resort, you might have to do a reinstall, however, I think that's unlikely. Do you have your data partition, data folders and files backed up onto available and trusted external media?