ok, try this...
First, go to any page (like www.google.com) and clear your browser's cache (don't worry about deleting cookies, just the files), then close your browser and start it again. Once that's done, make a file with just this in it:
<HTML>
<BODY>
Hello World
</BODY>
</HTML>
Then make a file with:
<HTML>
<BODY>
<?php echo phpinfo(); ?>
</BODY>
</HTML>
Then make a file with:
<HTML>
<BODY>
<?php echo "Hello World"; ?>
</BODY>
</HTML>
Try all of those, as well as trying your test.php file again, and tell me which (if any) work.
Just to clarify: You said that PHPMyAdmin DOES work?