Windows 8.1 freeze on startup (Inspiron 15 - 7537)

Hi guys! I have a huge problem. (Sorry for my english) The day befoe yesterday I had a Dell Update shown up on my taskbar, I approved it, it ran, and after that I could not turn my laptop on.

When I try to start it shows me the dell boot screen and it freezes at the login screen OR at desktop OR already at a blank screen before login.

I tried everything, I cannot get to the recovery screen, because somehow Windows thinks that it will boot, and doesn't offer me the recovery option. I didn't made a recovery disk, I have no optical drive, and I had no spare USB drives when I bought the laptop, after that I have forgotten.

I tried to make a bootable Windows 8 installation kit on USB, I manage to start it in UEFI mode, System restore cannot succeed, because it cannot access the Windows installation. Auto repair will also not work.

In command prompt I tried to rebuild the boot record, it cannot find any Windows installation (Total identified Windows installations: 0)

I tried to remove C:\Boot\bcd after a tutorial, it says, Path not found - C:\Boot

bcdboot c:\windows (file:///c:/windows) /s c: will also not work, it just doesn't recognize the command.

I started a bootable USB with partitioning software. It finds all my drives and all my volumes. OS partition seems to be all right. I wanted to rebuild MBR with the partitioning software, but it can rebuild only MBR and no GPT. At this point I am not sure if I may do it, i want to keep the bootloader in GPT.

I would be able to save some data from the disk, but I don't know if I may reinstall windows from the USB installation kit. I think it may be a partition with the original DELL installation kit, and I don't want to use all the DELL tools from my windows. The best would be to preserve this windows installation.

Can anybody help me further?