Hi dorsa,
Check this example. Now please take its reference and correct your code.
HTML
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript">
$(function () {
var current;
$('.Validate').on('keyup', function (e) {
current = $(this);
if (current.val() == 0 || current.val() == 'null') {
$(".Validate").each(function (i, item) {
if ($(current)[0].id != $(item)[0].id) {
if ($(item).val() == '') {
$(item).attr('disabled', 'disabled');
}
}
});
if (current.val() != '') {
$('[id*=TextBox8]').focus();
}
} else {
$(".Validate").each(function (i, item) {
$(item).removeAttr('disabled');
});
}
});
});
</script>
<div>
</div>
<asp:TextBox ID="TextBox1" runat="server" CssClass="Validate"></asp:TextBox>
<br />
<asp:TextBox ID="TextBox2" runat="server" CssClass="Validate"></asp:TextBox>
<br />
<asp:TextBox ID="TextBox3" runat="server" CssClass="Validate"></asp:TextBox>
<br />
<asp:TextBox ID="TextBox4" runat="server" CssClass="Validate"></asp:TextBox>
<br />
<asp:TextBox ID="TextBox5" runat="server" CssClass="Validate"></asp:TextBox>
<br />
<asp:TextBox ID="TextBox6" runat="server" CssClass="Validate"></asp:TextBox>
<br />
<asp:TextBox ID="TextBox7" runat="server" CssClass="Validate"></asp:TextBox>
<br />
<br />
<br />
<br />
<asp:TextBox ID="TextBox8" runat="server"></asp:TextBox>
Screenshot
