not able to enter value again in datagridcell

Question

Initially am able to enter data in datagrid. then I have displayed data to datagrid from database. To fill next data I have cleared datagrid throght below code 

 

if (this.dataGridView1.DataSource != null)

{

this.dataGridView1.DataSource = null;

}

else

{

this.dataGridView1.Rows.Clear();

this.dataGridView1.Refresh();

}

 

It empty's grid but am not able to enter new value manually to datagrid.

could please somebody help me to resolve the issue