When using Internet Explorer 8, it is not possible to fill in a "Contact Form" in Web Presence Builder 11.0. It's like something is preventing the focus from the form fields.
The problem is caused by improper presentation of CSS style in Internet Explorer 8 which was created by WPB during the site creation.
The problem has been fixed since version 11.5, bug is 133222.
Upgrade Parallels Web Presence Builder to the latest available version.