thx for replies,
I tried sfc /scannow but at the end of the verification it says that there are found some corrupted files but system cannot fix them, and solution with the dvd inside also doesn't work.
The problem is with icons, 3 days ago I started my pc, and some icons (ex. icon for folder) were changed, then I checked shell32.dll file by trying to change the icon for one folder and some icons were different from original ones. I think some software must have changed shell32.dll, and I think think replacing shell32.dll from someone elses system would be the fastest method. I can easily replace the file from xp (I have dual boot)