Can't access most programs from program (x86)/Program/ProgramData

Yesterday I noticed that I couldn't launch a program since my computer couldn't find the file "LIBEAY32.dll" and checked what could cause this.
Then I noticed that my antivirus "System Center Endpoint Protection" wasn't running, tried to start it, but no matter what methods I tried I could not launch it. The only thing that happens is that I get an error saying that it couldn't find "C:\Program Files\Microsoft Security Client\msseces.exe". The same happens when I try to run Windows Defender.
I can't uninstall most programs from my computer since all that happens are that Windows Installer tells me "The feature you are trying to use is on a network resource that is unavailable", which prevents me from installing another antivirus to check if that can solve the problem. (I did manage to install Advanced System Care 8 pro, but after a scan and repair the problem is still unsolved.)

All folders in C: is "read only" and I've tried setting myself as owner and give me full authority to every file on the computer (a few hundred/thousand files didn't set me as owner unless i did it file by file, only .dll files in different as far as I know (C:\Program Files\Common Files\Microsoft Shared\ink\InkDIV.dll for example)), remove the read only and nothing changes.
I noticed that an unknown user named "S-1-15-2-1" had access to most of these files. Don't know if this has anything to do with it, googled around on this and it may be malicious.

I've been trying some other things that I can't recall at the moment, but if anyone knows what the problem could be/has a solution to it I would be very happy.

I have this problem on my Lenovo Thinkpad T520 with Windows 7 Enterprice x64.

If any more information is needed please ask.

DarKnight said:

You should try to restore your computer to an earlier time

Yeah, I've already tried this, but I can't access the system recovery. :/

I'll probably ghost it if I can't find the problem in a few days.