I'm writing this post for two reasons: 1) I fixed my PC so it might help others. 2) The pros here could maybe explain further how what I did helped. Well, to explain the problem: I have a C: drive and a D: drive. Lately, on startup I would find a strange cmd window opening automatically w/ a title like this: C:\windows\..\cmd C:\.X And Control Panel in the startup menu wouldn't appear. A CTRL-ALT-DEL won't bring up the task manager and opening any text file using notepad would always give " File is being used by another program". Registry Editor is restricted by administrator. Since I had nothing valuable on C:, I decided to carry out a clean FORMAT and re-install Windows. I did that twice. And right after installing windows, as soon as I perform my first reboot, the exact symptoms appear again. I followed the 8 steps to the point, but nothing would be found, neither on C: or D: drive. I ran ComboFix.exe but it would finish and reboot and no real change. I kind of followed around and got the hint that a process C:\.X.exe is the main culprit. But it was impossible to find it and delete it or kill it. The solution was by using a software called Unlocker. I went to C:\windows\system32\regedit.exe and found that .X process locking it. As soon as I killed the process .X, I could actually do everything. But upon restart, again, same symptoms. The trick was the combination of: 1) Unlocking regedit in windows and deleting it. 2) Unlocking notepad. 3) Running ComboFix after that. After that restart, It was finally totally removed. That's it. Pros, your comment.