While editing pages on your SharePoint sites you probably encountered a situation when the ‘Edit page’ option in the Site Actions menu is disabled (greyed-out)!
This is not an error. Edit page command will be disabled when another user has checked-out that particular page. To see which user has done so you will need to navigate to Pages library on your site.
If you have the right permissions and you need to edit the page, you can show the page editing toolbar and then click on Page -> Override Check Out. This will undo any changes the other users has made and the page will be checked out to you, but is useful if you really need to make a modification to the page.
However, If the Edit Page option is MISSING all together it is because MS decided to remove that option for that page for some reason! There is a hack, just append ?ToolPaneView=2 or ??ToolPaneView=2 to the end of the URL.