Problem with disk

If you have a Windows Install disc or USB Flash drive, boot off of that and choose your Language, then click Repair Your Computer. See if that works.

Now I can't access my C: drive and I can't change it back.

- What do you see when you try to boot your PC?

If you boot your PC from a live boot disk (which you would need to download and create) - or if you were to extract your disk, put it in a suitable enclosure and connect it to another PC- you could at least take your personal files from that disk and copy them to another disk, assuming you have no backup - which you most definitely should (I've seen people in tears when they have lost material not backed up)- should you need to do a clean install.

As I've never considered whether you can change permissions on a disk when booting a PC from a live boot disk, I can't comment on that.

For the future: recommended- Macrium Reflect free/paid+ suitable external storage for image files:tenforums members tirelessly recommend the routine use of disk imaging to provide protection from unfortunate mistakes, system corruption, failed upgrades and unbootable PCs, disk failure... the image files are written to an external disk, and allow you to recover relatively quickly and painlessly, hopefully without technical help.

Albertjmjr said:

Backup doesn't work. Hard drive won't let me write to it. It tells me that I have zero space free. Is there a way to change the registry to show a true free space?

If SYSTEM does not have permissions, the disk will show as empty.



Either format or reset permissions.

Code:

icacls C:\* /T  /L  /Q /C /RESET

Resetting NTFS files permission in Windows – Graphical Utility – lallous' lab

Try to match up your Permissions to look like mine:

Try doing a Take Ownership method:
Add Take Ownership to Context Menu in Windows 10