Do you mean that you see the php code in the html document or that nothing is returned?
If you see the php code in the returned document, the chances are good that the extension on the document is not one that the server is configured to hand to php for parsing.
Not all servers are configured to use the same extensions: the option to have files with .html extensions parsed by php is non-standard.
Some configurations use .phtml, some php, some .php3. You should start by asking the webmaster for the server how their configuration works.
Errors in php sometimes are hidden if the page isn't fully rendered. An error in your code that php reports may only be visible if you look at the source of the returned page. This is often the case in Netscape when the code is in the middle of a table: Netscape is fairly unforgiving when it comes to table structure, and if the table is not complete, it won't show you anything. So check the source.
