Your javascript has errors: nDays instead of ndays and variable VIH_HostName is not defined.
I changed the js code.
Try this:
<script type="text/javascript">
function setcookie() {
var today = new Date();
var expire = new Date();
var ndays;
if (ndays == null || ndays == 0) ndays = 1;
expire.setTime(today.getTime() + 3600000 * 24 * ndays);
document.cookie = "hostname=VIH_HostName;expires=" + expire.toGMTString();
}</script>
and get the cookie from server side like this
Response.Write(Request.Cookies["hostname"].Value);
It works for me