How to open an excel file

Hello,


        I have Microsoft.Office.Interop.Excel add as a Reference as well as
Microsoft.Office.Core and I have the following line of code:

private Microsoft.Office.Interop.Excel._Application ExcelObj;
ExcelObj = new Microsoft.Office.Interop.Excel._Application();

And I get the error
Cannot create an instance of the abstract class or interface
Microsoft.Office.Interop.Excel._Application

What am I doing wrong???