Hello everyone,
yesterday I tried to upload sketch, but suddenly something went wrong and code was't uploaded. So I'm suspicious that there is something wrong with atmega16u2. Bootloader is working, because I tried to push reset button and L LED blinked as normal. There is one more thing, that Arduino uploader recognized Port COM. Any advice would be appropriate. 
By the way, microcontroller is working too, because a code was uploaded and its working, but USB isn't. I tried different USB wires and different PC's but I got a same results.
I don't understand what you are saying. If you can upload code then the USB is working. What makes you think it is not?
I mean I uploaded a sketch, before Arduino had crashed.
So that suggests that either the 16u2 is toast or it has had it's boot loader corrupt or the PC driver is corrupt.
Try reflashing the boot loader.
I can't enter to DFU mode, then I short 2 pins near atmega16u2 nothing changes. By the way, will I be able to upload sketches through bluetooth without atmega16u2?