I've upgraded a SharePoint 2007 (220.127.116.1121) database to SharePoint 2010 (no SP's or anything yet) and I noticed that there is no edit button that brings up the ribbon to edit a page in the upgraded SharePoint 2010 site. If I create a new site and new collection I get the edit button. If I create a new site collection under the upgraded 2007 web application I get an edit button, but I cannot seem to figure out how to enable this functionality on the upgraded sites. I've been banging my head against this all day.
I think that the problem here is 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.
The missing edit button might be due to many causes: 1. You haven't been doing Visual Upgrade (which actually replaces your master page with the v4.master) 2. 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)!
If it happens in SharePoint 2013, try an play with your browser compatibility mode.