How can I restore permissions to my C:\ drive?

[tvandinther]

Hi, I made a silly mistake.

 

I have two Windows 10 installs. My new primary install (OS A) is on an NVMe drive, and an old install (OS B) is on a 2.5" SSD. My PC can boot to either OS, so I logged onto OS B and started ripping some data out and backing up the files I wanted to keep. This effort is in preparation for completely removing the old install. Nothing from OS B is on the new NVMe drive, so to prevent me from making mistakes, I thought to remove modify permissions from this drive (allocated as E:\ in OS B), thinking it would only stop OS B from making changes. The moment I clicked confirm, I realised that it might not actually go to plan, so I quickly cancelled it. So now, some files have had their permissions changed, but not all. OS A still boots, and I can access quite a few files on the NVMe drive (C:\ in OS A), but only if I access them through paths that still have permissions; I can not browse from the root of C:\. I figure that this should be an easy fix. I could modify permissions again from OS A and set ownership of the disk, and revert the permissions. Unfortunately, when trying to elevate to Administrator privileges on the "Advanced Security Settings for Local Disk" window, there is a long delay (a few minutes) followed by an error message regarding not having permissions to access a specific file on C:\ required to elevate privileges.

 

I enlisted GPT4 to run me through a recovery plan and audited the commands it suggested. It all seems above board and mirrored some advice I saw on answers.microsoft.com. The plan included running commands from safe-mode command prompt such as:

net user administrator /active:yes

takeown /F C:\ /R /D Y

icacls C:\ /grant:r "Administrators:(OI)(CI)F" /T

icacls C:\ /inheritance:e /T

These commands ran successfully, and I was hopeful the problem was fixed. Alas, the issue persists. So I am reaching out for some tips to fix this without losing all of the data and OS settings. What should I do?

Thanks.