Ok, you need to provide us with more information.
1) check the /var/log/message to see if there is any vnc relate error message
2) in a console, run
bash -x /etc/init.d/vncserver
- this will print detailed information about how vnc is started
Capture these information and post it here again
However, before you go thru this, you can actually try vncpasswd
first. It is very likely that you did not set the password for the login which will use vnc. Check vncpasswd documentation for more detail