Thanks for your information. Please leave me a message next time on http://www.q2apro.com/plugins/best-users-pro or http://www.q2apro.com/forum/ where I will see your message immediately. By accident I stumbled over your post here on the question2answer forum...
To your problem:
1. It is hard to tell what the problem is without seeing your site. Please provide your domain either as comment or by sending me a private message. Is this your site: http://czporadna.cz/ ?
2. Have you noticed any error messages? And checked your server error_log?
3. Do you use a custom theme?
4. What entries do you see in database table qa_userscores?
Update: I guess you did change the point system after installing the plugin? Because you mentioned "recalculation".
Please read the notes: http://www.q2apro.com/plugins/best-users-pro#notes
Before installing the plugin, please think about your point system (>Admin >Points). The points should not change over time, as the plugin stores recent userpoints every month. If you change userpoints later on, the userscores shown for the recent month could be incorrect (or even negative).
When the plugin got installed, the widget will be empty. Wait for the first score event (question, answer, vote) and you will see the users listed in the widget.
After the first installation, for the first month you will see the total score for each user as the monthly score. This is due to the design of the plugin, it saves the total scores each month and calculates the differences which then become the monthly scores. In other words, after the first month, starting on 1st of the next month, all users will start with 0 points for the new month. (Of course, the total user scores remain.)
If you changed the point system, users probably have negative scores now. This is why there is nobody showing up in the widget.
To solve this issue, you can:
1. Change the point system back.
2. Empty the entire table for a restart.
See here for details: http://www.q2apro.com/forum/247/help-with-best-user-per-month?show=266#c266