using System;

using System.Xml;

using System.Xml.Linq;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var xml = @"<ArrayOfHROps_User xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:xsd=""http://www.w3.org/2001/XMLSchema"">

  <HROps_User>

    <EntityKey>

      <EntitySetName>HROps_User</EntitySetName>

      <EntityContainerName>HROperationsEntities</EntityContainerName>

      <EntityKeyValues>

        <EntityKeyMember>

          <Key>UserID</Key>

          <Value xsi:type=""xsd:int"">44405</Value>

        </EntityKeyMember>

      </EntityKeyValues>

    </EntityKey>

    <UserID>44405</UserID>

    <EmployeeID>AAA40</EmployeeID>

    <Period>2015-06-17T00:00:00</Period>

    <Active>true</Active>

    <Options>false</Options>

    <Pager>false</Pager>

    <Contractor>false</Contractor>

    <TimeStamp>2015-06-18T13:37:38.3</TimeStamp>

    <UserName>Mark.Walsh</UserName>

  </HROps_User>

  <HROps_User>

    <EntityKey>

      <EntitySetName>HROps_User</EntitySetName>

      <EntityContainerName>HROperationsEntities</EntityContainerName>

      <EntityKeyValues>

        <EntityKeyMember>

          <Key>UserID</Key>

          <Value xsi:type=""xsd:int"">44406</Value>

        </EntityKeyMember>

      </EntityKeyValues>

    </EntityKey>

    <UserID>44406</UserID>

    <EmployeeID>AAA60</EmployeeID>

    <Period>2015-06-17T00:00:00</Period>

    <Active>true</Active>

    <Options>false</Options>

    <Pager>false</Pager>

    <Contractor>false</Contractor>

    <TimeStamp>2015-06-18T13:37:38.94</TimeStamp>

    <UserName>Mark.Walsh</UserName>

  </HROps_User>

</ArrayOfHROps_User>";

        var myxml = XElement.Parse(xml);

        var result = myxml.Elements().FirstOrDefault(x=> (string)x.Element("UserName") == "Mark.Walsh");

        Console.WriteLine(result.ToString());

    }

}