If you are really sure about the excel as your backend.
Try this to add into your appconfig section in app.config or web.config file.
<add key="ExcelConnectionString" value="OLEDB;Provider=Microsoft.Jet.OLEDB.4.0;Data Source=[Your excel file path here];" />
Example
<add key="ExcelConnectionString" value="OLEDB;Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\excel.xls;" />
in your code behind add this
string constr = ConfigurationManager.Appsettings["ExcelConnectionString"];
this way you can always change the path of the excel without rebuilding your project.
and try to be more resourceful. use the google.