Can't get past lock screen on Windows 10 after upgrading from Win 7 (free upgrade)

[dynamic.czech]

Hello, few days ago I've upgraded from Windows Vista Home Basic, to Windows 7 Home (using .iso file on bootable USB drive) and then used the free upgrade to Windows 10 Home without any DVD/USB, just Media Creation Tool, located on C: disk. Installation and everything worked fine, it said that Windows was activated and lincense is ok, all seemed to work. So I put the PC (not a laptop btw) to sleep mode over night. Next morning when I turned the PC on from sleep mode, I still can't get past the locked screen (there is a photo of Venice, Italy I guess that doesn't change, time and date in the left corner that works and some two icons in the bottom right corner but NOT the power icon).

Mouse and keyboard work, meaning that the screen reacts to me hitting buttons, but all it does is slide the screen to the top, the login picture appears for a split second and then goes back to the lock screen. I've tried turning the PC off completely 3 times so after the 3rd start it said "Your PC ran into a problem and needs to restart. We're just collecting some error info, and then we'll restart for you." and then it restarted on it's own, said it's updating something and then went back to where I was, still stuck on the lock screen. Pressing Ctrl+Alt+Del/Esc, Shift, Shift+F5, F4, Windows+X, Win+R either at the locked screen or during restart didn't work.

I really don't know what to do at this point, because I can't go into safe mode, I can't access any Automatic repair window, I think I can't do a clean install because I don't have a Win 10 license and I want to keep my data on my HDD and I don't know how can I go back to Windows 7, because apparently I can only install it once (it's been previously installed on a different computer). I'd like to keep Windows 10, cause it will have support till 2025 unlike Win 7, and wouldn't really want to reinstall everything on that PC if I had to do a clean install..

Any help is greatly appreciated. Thank you in advance

 

[rgd1101]

download windows 10 iso. https/www.microsoft.com/en-us/software-download/windows10
boot from it and do repair

 

[dynamic.czech]

download windows 10 iso. https/www.microsoft.com/en-us/software-download/windows10
boot from it and do repair

Thank you very much for the answer. Although the solution was not that simple. Booting from the USB with Windows 10 iso on it helped me to get to the Repair menu, but none of the Windows' automatic repairs worked, one put me into infinite boot loop. So I had to use the command prompt and restore from a system restore point using a couple of commands.

Here are the commands (in order) for those who had the same problem as me:
cd c:\Windows\system32\config (press enter after typing every command)
ren SYSTEM system.001
ren SOFTWARE software.001
Rstrui.exe /offline:C:\windows=active

System restore should work and allow you to restore to the point where Windows still worked normally. When in Windows, I bypassed the lockscreen and login window (I recommend that only if you use a desktop PC) so when I restart the PC or it wakes up from sleep mode, it goes automatically into windows and I'm not stuck at lockscreen anymore. Other thing was, that Windows update tried to install some update but an error always popped up and didn't install. So use Windows to diagnose and fix the problem with Windows update (worked for me thankfully). And finally, run the Command Prompt/PowerShell as Administrator again and type in these commands:
sfc /scannow (press enter and let it finish and if it tells you to restart the PC, wait and type in following cmd)
DISM /Online /Cleanup-Image /RestoreHealth (enter again, let it finish and then if you've done all above, Windows should work without problems)

Hopefully this helped those who got into the same unfortunate situation as me. If you have any questions regarding my solution, I can try to help but can't guarantee anything.