Remove ‘My Orders’ box in magento

Try to look into sales.xml:

<customer_account>
        <!-- Mage_Sales -->
        <reference name="customer_account_navigation">
            <action method="addLink" translate="label" module="sales"><name>orders</name><path>sales/order/history/</path><label>My Orders</label></action>
        </reference>

    </customer_account>