OnBlur of the Textbox call a javascript function say 'fnCheckInput'.
function fnCheckInput()
{
var controlValue = document.getElementById('TextBox1').value;
var s = parseInt(controlValue);
if(s == 0)
{
document.getElementById('TextBox1').value = "";
return false;
}
return true;
}
Here is your HTML:
<asp:textbox id="TextBox1" runat="server" onblur="return fnCheckInput();" xmlns:asp="#unknown"></asp:textbox>
And also, you need to ensure that only numbers should be entered in TextBox. Use some validation control for that.
--Amit