Windows 8 "chkdsk /r" stuck on stage 4

I know that there are many questions about this topic but I think my situation is a bit different and since I'm a newbie, I'd need some tips and help specific for my case.

I have a Windows 8 pc which was not starting anymore. It's an Asus SonicMaster. At BIOS runtime it says that Windows is not able to start and I tried some of the advanced options:

1 - Recovering it for a restore point: it says that it is unable to do that; 2 - Updating it: it says the it can't do that since the disk is locked (I actually have no idea about that); 3 - Maybe I have done some other trials I don't remember now, but basically nothing worked for me.

Then I found a tutorial online suggesting to run chkdsk /r. Thus, in the advanced options I chose the command line prompt and I run it on the C: disk. The result is that now it has been stuck for more than 12 hours on stage 4. At the beginning it was stuck on 14 percent but the number of files processed was growing up. But after few minutes the number of file got stuck too and now it has been stuck on 179408 for more than 12 hours.

I read over the Internet that stopping chkdsk is highly unsafe, but basically I don't know what to do right now. Can anybody help me?

As a side question, the command line showed me to be in the X: partition, where from the fs tree structure seems to be installed a Windows with no users... Actually the real boot partition is C, where the user is present... Do you think this may be the root of the issue that I am not able anymore to start Windows? If so, I tried to change the boot partition from the Boot Menu, but it's not feasible since the only option there is "Windows Boot". How can I change the boot partition?

* UPDATE *

Due to a power down, the pc shut down. Then, when I booted it again, nothing seemed to be changed. Thus, I followed this tutorial: How can I repair the Windows 8 EFI Bootloader? and now I'm lost!

Now it comes out a blue screen with the error message:

File: C:\Windows\system32\config\system
Error code: 0xc0000185

Pressing F8 to get the boot option doesn't work, since it comes back to this page. What can I do?

Thank you very much, Marco