myButton.Click += (sender, args) => {
    if (!this.DataGrid.Enabled) {
        this.DataGrid.Enabled = true;
        this.DataGrid.ClientSettings.EnablePostBackOnRowClick = true;
        this.DataGrid.ClientSettings.Resizing.AllowColumnResize = true;
        this.DataGrid.ClientSettings.Selecting.AllowRowSelect = true;
        this.DataGrid.ClientSettings.AllowKeyboardNavigation = true;
    } else {
        this.DataGrid.Enabled = false;
        this.DataGrid.ClientSettings.EnablePostBackOnRowClick = false;
        this.DataGrid.ClientSettings.Resizing.AllowColumnResize = false;
        this.DataGrid.ClientSettings.Selecting.AllowRowSelect = false;
        this.DataGrid.ClientSettings.AllowKeyboardNavigation = false;
    }
    this.DataGrid.Rebind();
}

[GridException: Please set ClientSettings.Selecting.AllowRowSelect to "True" to start using GridClientSelectColumn.]

<ClientSettings>
  <Selecting AllowRowSelect="True"></Selecting>
</ClientSettings>

<telerik:RadGrid ID="mygrid"
                 runat="server" AutoGenerateColumns="false"
                 AllowSorting="true"
                 OnNeedDataSource="mygrid_NeedDataSource"
                 AllowFilteringByColumn="False">
<ClientSettings>
  <Selecting AllowRowSelect="True"></Selecting>
</ClientSettings>
<MasterTableView DataKeyNames="myColumn" Name="PoHeader">
  <Columns>
    <telerik:GridClientSelectColumn ItemStyle-Width="25px" />
    <telerik:GridBoundColumn DataField="myColumn" HeaderText="My Column" />
  </Columns>
</MasterTableView>