You need to specify
DisplayMemeberPath
Binding
(or similar) for each columns in the DataGrid
Update 1:
Did you binded the lArrObjclsGridLoadExcelData object to the DataGrid's ItemsSource property?
You can binding like,
dgrIncidents.ItemsSource = lArrObjclsGridLoadExcelData;
or
Binding binding = new Binding();
binding.Source = lArrObjclsGridLoadExcelData;
dgrIncidents.SetBinding(DataGrid.ItemsSourceProperty, binding);