password characters not showed at input

[Marcomassimo]

I have just purchased a VPS; it is the first time for me;
the VNC session works fine entering server:port and VNC password.
Instead in the server console the login (root) is accepted, but the password is not.
At the prompt (password:) i press the key of the password on the keyboard, but the cursor is always blinking on the same position and not any charachter is showed.
This strange issue is there not only for UltraVNC but in others VNC client too.
Some advice? Thank you