No access to my C: drive or any flies that are on the drive

Hello
A few hours ago I downgraded to windows 7, as I just can't stand windows 10. The downgrade went smoothly, and before I knew it I had windows 7 reinstalled. I installed the Realtek ethernet driver needed for me to get on the internet, and I started to download windows updates. ~197 updates were found, and I started downloading them right away. While the PC were downloading the updates, I installed Avast, Skype, Steam, Spotify, Discord and CS 1.6. The updates were half done when I had installed all of the previously mentioned programs, and I left the pc for about an hour. When I came back, the pc said that ~159 updates were successfully installed, and the rest failed. I then restarted the pc, and it took some time to restart, as windows were configuring the updates. When I logged into my windows 7 admin account, I noticed that the pc's desktop was black, and that my icons didn't pop up right away. Then came some errors such as: api-ms-win-downlevel-user32-l1-1-0.dll, and api-ms-win-downlevel-ole32-l1-1-0.dll. I noticed that I couldn't open any of the previously installed programs, and I also couldn't access my C: drive. I can't open any programs as an administrator, even though I've followed 10+ guides saying that I should change the security settings, and change ownership of the drive. That doesn't seem to work at all, and I can't enable the hidden admin account either. I don't know what to do at this point, as it doesn't seem like I have access to download or install programs, as google chrome doesn't want to load any pages, and Internet Explorer doesn't open, because of the API error mentioned earlier.

I have no clue what went wrong, and I am in desperate need of help. I will link a video I uploaded on youtube, where all the different errors can be seen. Please help me, thanks!

https://www.youtube.com/watch?v=3m_QG9p1f6A

Sorry if this is posted in the wrong forum, please point me to the right forum if this is the wrong one.

Thanks !

And btw, windows 7 were installed from a bootable USB made with Rufus.

I can't see the video very well as on phone. What exactly did you do with permissions it sounds as if you have locked Windows out from the drive. You need to try adding system to full control of the drive. Post a full list of permissions on c . The other thing could be the drive is corrupted try running from a cmd prompt chkdsk c: /r if you can't do it in Windows boot install and get a prompt that way

Thanks for the reply samuria,

If I try and run the command in cmd, it comes up with an error saying: Access is denied.
SYSTEM has full control, and every possible permission allowed, except special permissions, which cant be enabled for some reason.

I just tried booting onto the USB and enabling the cmd from there, and then i get this error: /r is not recognized as an internal or external command, operable program or batch file.

You are typing
Chkdsk c: /r space between c: and /

Or try
Chkdsk c: /f

Are the permission on Windows folders all set as system full control

If you do a clean install its best to delete all paritionsand let windows create new one and format it then there is no chance permissions could effect it

Also, if you do a clean install, the first thing you should do is get a good backup. That way, if this happens again, you'll be able to easily recover.

Then, when you have everything installed and updated, and if all is working well, do another good backup.