I've create a custom admin module but i can't put a content in it, it always is blank i'm trying with a simple code for test, but nothing seem to work

public function indexAction()
{
    $this->loadLayout();

    $this->_addContent($this->getLayout()->createBlock('adminhtml/template')->setTemplate('uhmaadmin/contactos.list.phtml')->toHtml());
    $this->renderLayout();
}

. PHTML bir

echo 'hello world';

but doesn't print nothing, if a make an error in the phtml, the system crash, it means that its getting the file, but, what i'm i missing please, help