Hi,
When you instantiate the ClientCredentials, use DefaultNetworkCredentials. The following code should do the work:
IOrganizationService orgService = null;
ClientCredentials credentials = new ClientCredentials();
credentials.Windows.ClientCredential = System.Net.CredentialCache.DefaultNetworkCredentials;
Uri serviceUri = new Uri("http://mycrm:5555/MyOrg/XRMServices/2011/Organization.svc");
OrganizationServiceProxy orgServiceProxy = new OrganizationServiceProxy(serviceUri, null, credentials, null);
orgServiceProxy.EnableProxyTypes();
orgService = (IOrganizationService)orgServiceProxy;
Make sure you replace the Uri with that of your CRM Server URL.
Admin QuikView Solution for CRM 2013