U can use javascript...........I had this problem before and to my knowledge this is the best solution.
Do this in Code behind - cs file
ClientScript.RegisterStartupScript
(GetType(),"Javascript", "javascript: ShowButton(); ",true);
DO this in your javascript - aspx file
<script>
function ShowButton()
{
var btn = document.getElementById("para1");
btn.enable = 'true';
btn.disabled = 'true';
}
</script>