How include two php file using hook location global_start

[mondingnibai]

I want to ask how to include two php files separately?using the hook location global start?
Right now, I have two plug-in code namely firstplugin and secondplugin with same code. See below:

firstplugin code:

ob_start();
include('firstplugin.php');
$first= ob_get_contents();
ob_clean();

secondplugin code:

ob_start();
include('secondplugin.php');
$second= ob_get_contents();
ob_clean()

Now, when I activate this two plug-in nothing shows up except for a white backgroud in the browser. Now, when I deactivate either one of the two it works. I run this two plug-ins in one page. I want them to show up. How can I achieve this?How can I include two php files with same code and the same hook location?Need Help ASAP...