[Lynne]

In global.php is this code which I'm sure you can modify for your own needs:

// check that board is active - if not admin, then display error
if (!$vboptions['bbactive'] AND THIS_SCRIPT != 'login')
{
	if (!($permissions['adminpermissions'] & CANCONTROLPANEL))
	{
		$show['enableforumjump'] = true;
		eval('standard_error("' . str_replace("\'", "'", addslashes($vboptions['bbclosedreason'])) . '");');
		unset($shutdownqueries['lastvisit']);
	}
	else
	{
		// show the board disabled warning message so that admins don't leave the board turned off by accident
		eval('$warning = "' . fetch_template('board_inactive_warning') . '";');
		$header = $warning . $header;
		$footer .= $warning;
	}
}