Accessing External Data from SharePoint 2010

I want to access external data from my SharePoint site.

I'm told that I need to follow these two articles.

http://msdn.microsoft.com/en-us/library/ff953161.aspx
http://msdn.microsoft.com/en-us/library/ff625800.aspx

I followed the first article but I get this error when I open the external list in my SharePoint site:

"Unable to display this Web Part. To troubleshoot the problem, open this Web page in a Microsoft SharePoint Foundation-compatible HTML editor such as Microsoft SharePoint Designer. If the problem persists, contact your Web server administrator."

I don't know how to write a custom code

BTW I have installed PowerPivot on my SharePoint server.

Can someone please help me? I need to do this very quickly.