I am using SharePoint Designer 2010 to create a new master page. I duplicated my v4.master and then added a couple of lines of text and a picture to the Main Place Holder area. Then when I try to make a page from the master I get the message that I have to edit the page in advanced mode. When the editor opens up there is only two lines of CSS and I am unable to add anything to the page. I tried making a page from the v4.master which I have not touched and get the same problem. I do have publishing enabled and have full control permissions for the entire site.
Two things; firstly, you're not creating a page based on a masterpage. The masterpage is set at the web level, not at the page level. What you're likely seeing is that the page layout you're using for the page doesn't contain any editable regions within SharePoint Designer, thus it wants you to put it into edit mode. Most of the time you're going to create a custom page layout for things like your homepage. The page layout sits on top of the masterpage and contains the actual containers for webparts, rich text, etc. Those elements don't actually sit on the masterpage itself. Header/footer/navigation/etc. is contained within the masterpage. The page layout contains the structure of the actual body of the page.
Secondly, SharePoint Designer is arguably the worst thing you can use to brand a SharePoint site (especially if you've started editing things in advanced mode). Once you customize a page using SharePoint designer, you separate that page from the original file definition that Microsoft ships with SharePoint. That file now lives in the content database, and is associated with this specific site collection where you've set it up. This becomes an issue in two scenarios: the biggest of which is when you decide to upgrade SharePoint 2010 to 2013. Now that you have non-solution based customizations, there becomes a HEAVILY manual process that you have to go through to manually remove all of those customizations to make sure that your site can upgrade without errors (since the upgrade process hits every file in the content database). The second scenario is if you need to make changes to the solution (such as a copyright year in the footer, or a color change). When you brand with SharePoint Designer, you have to manually make that change on every site collection.
The best practices approach to branding is to deploy a SharePoint solution package (WSP file) to the environment that contains a site feature to enable your branding. This is repeatable across multiple sites/server farms, and is much cleaner to upgrade when the time comes.