Hi,
I know you said you read the documentation, but, I feel I must ask this question. Do you have the following in your layout.master (as described in the "Understanding the Layou.master" docs)?
<asp:Panel id="divLeft" runat="server" cssclass="leftside" visible="True" SkinID="pnlPlain">
<asp:contentplaceholder ID="leftContent" runat="server"></asp:contentplaceholder>
</asp:Panel>
<asp:Panel id="divCenter" runat="server" visible="True" cssclass="center-rightandleftmargins" SkinID="pnlPlain">
<asp:ContentPlaceHolder ID="mainContent" runat="server"></asp:ContentPlaceHolder>
</asp:Panel>
<asp:Panel id="divRight" runat="server" visible="True" cssclass="rightside" SkinID="pnlPlain">
<asp:contentplaceholder ID="rightContent" runat="server"></asp:contentplaceholder>
</asp:Panel>
To be clear, you need those items somewhere in your layout.master; if you leave any of them out, you will not be able to see content on your site at some point.
HTH,
Joe D.