In SharePoint we don’t have edit page options [ribbon toolbar page edit formatting options] for all types of page for application page we cannot edit like site pages so The missing edit button might be due to many causes:
Can you verify that it’s not a permissions issue? Try navigating to the page in edit mode by appending to the url: your-site/Pages/YourPage.aspx?ControlMode=Edit&DisplayMode=Design
Or you can try this
1. You can check that on some pages the ribbon is hidden by default. You need to make it visible by clicking on “Show Ribbon” on the “Site Actions” drop-down menu.
2. You haven’t been doing Visual Upgrade (which actually replaces your master page with the v4.master)
3. If you have different master page and may be your master page is not 100% compatibile with SP2010, nor does it use the elements from v4.master (collaboration) or the example nightandday.master
To add the button in your page you could use the <SharePoint:PageStateActionButton id=”PageStateActionButton” runat=”server” Visible=”false” /> (if you’ve seen already that would generate the button on the left side of the ribbon)!