MySQL Error 1046

Hello,
I hope that you can help me.
I was in the middle of setting up a php based guestbook from "proxy2.de" when I received a series of error message when trying to access my site. As a result I deleted the guestbook and restarted the process. Now I cannot access my site by typing in the domain name. If I attempt to directly reach a page I am able to do so.

This error message:

MySQL Error : Database Error
Error Number: 1046 No Database Selected
Date : Sun, May 30, 2004 17:00:15
IP : xxx.xxx.xxx
Browser : Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; (R1 1.3))
Referer :
PHP Version : 4.3.6
OS : Linux
Server : Apache/1.3.31 (Unix) mod_auth_passthrough/1.8 mod_log_bytes/1.2 mod_bwlimited/1.4 PHP/4.3.6 FrontPage/5.0.2.2634 mod_ssl/2.8.17 OpenSSL/0.9.7a
Server Name :

What would I need to do in order to regain access to the site?