Thanks for all replies and help.
Unfortunatelly none of these works.
I tried repair, I tried to seek for viruses, I tried to sfc /scannow.
I think that the only solution is to reinstall..
And here have another question to You guys - what should I do to avoid these problems in future? Reinstall, then install all, most important programs and make an image copy of my system to be able to have everything back when I want ?
have You any suggestions here?
I also thought that in future I could install system on one partition, and programs on another.
But as far as I know, all programs have their files also placed somewhere in system partition, so while the system is damaged and needs to be replaced, I would also erase those files needed for programs to work, am I right ?
p.s. i'm still using safe mode, and it works fine
thanks for help!