HttpClient with WebApi is not working

I'm doing this:

HttpClient client = new HttpClient();
var retorno = client.GetStringAsync("http://localhost/painelapi/api/values/get");

gets WaitForActivation status but returns nothing to me.

so I made this way:

HttpClient client = new HttpClient();
var retorno = client.GetStringAsync("http://localhost/painelapi/api/values/get").ConfigureAwait(false);

and returns me isCompleted false

can help me?