Question

regular expression not to allow zero

it should allow 0.0000001 as value but should not allow to enter 0.

I need validator not javascript

Answer 1

I think all you need is this ^(?=.*[1-9])\d*\.?\d*$

But, you could get fancy and allow only a single leading zero if its before a decimal point.
^(?=.*[1-9])(?:[1-9]\d*\.?|0?\.)\d*$

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" 
     ControlToValidate="TextBox1" ErrorMessage="Input is not valid." 
     ValidationExpression="^(?=.*[1-9])(?:[1-9]\d*\.?|0?\.)\d*$"></asp:RegularExpressionValidator>
<asp:Button ID="Button1" runat="server" Text="Button" />