I've got a little problem, I've got a php file that start such as this:

<?php
ini_set("display_errors", true);
echo "test"; 
exit(); 

In some way this returns a clear page?!

I personally use ubuntu 10.10, gvim and apache2

Can this have something related to utf-8 formatting? I simply switched to ubuntu and gvim so I don't know basically use utf-8 or otherwise, but Yes, it continues to be recognized to cause this issue.

EDIT:

After I alter the file to

<?php
test

Nothing turns up, but when I change it out to:

test
<?php

test turns up ?!

Try changing the beginning of your script with this particular:

<?php
ini_set("display_errors", true);
error_reporting( E_ALL );
echo "test";

If you've still got an empty output, produce a new file and copy-paste this content from the faulty file across one line/section/control structure at any given time, performing the script after each section is moved. The section you transfer before getting an empty output is most likely your cuprit.

Also, try searching at the Error Logs - they might contain particulars from the error being experienced and leading to the blank output. (Actually, I'd do this first.)

Also, with regards to the code clips incorporated inside your original question:

<?php
test

Will invariably fail, because it is not correct syntax.

<?php
echo 'test';

Should lead to "test" being printed towards the screen.