Hi Krishna,
I think you want to validate the textbox,
at page load event you want to check whether text box has value or not,
Here is sample code you can make use of
protected void Page_Load(object sender, EventArgs e)
{
if (String.IsNullOrEmpty(txtbox.Text))
{
txtbox.Text = "Your string goes here";
}
else
{
Response.Redirect("About.aspx");
}
}
Hope this helps you a bit.
Regards,
RK