Suddenly, k2 Media Manager is empty. I can browse to pictures only from Joomla Media Manager.
I use J 3.3.6.

What's wrong?

Make sure you have set the correct root path for your images.This setting is located in K2's parameters.
Furthermore make sure that you have disabled error reporting.

Everything Is set correctly. I try to make some test. I upload picture using FileZilla and try to see them in joomla backend, but is it empty.
Path for images is default. Error reporting is set to NONE.

Help?

I disable NoNumber plugin and it is okay now. I don't know is that good solution?

Yes, since you got the media manager working.
This extension was most likely causing a JS conflict.
If you enabled it back check your browser's console tab for the error.