PHP error with regard to files

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PHP

$id=$_REQUEST['id'];
if($id == ""){
$id = "Home";
$ext = ".txt";
$path = "pages/";
$file = $_SERVER['/home/a7120106/public_html/'] . ($path . $id . $ext);
$contents = file($file);
$string = implode($contents);
echo $string;
}
else{
$file = $_SERVER['/home/a7120106/public_html/'] . ($path . $id . $ext);
$contents = file($file);
$string = implode($contents);
echo $string;
}

This is my code. When I try to load a page other than home for example: Videos. Which by the way exists, I get this:

Warning: file(videos) [function.file]: failed to open stream: No such file or directory in /home/a7120106/public_html/index.php on line 40
Warning: implode() [function.implode]: Argument must be an array in /home/a7120106/public_html/index.php on line 41

I am trying to load content from a text file onto the page using id tags.

Please help, Cheers