Maybe something like this will help?
SELECT ci.Name
,CASE WHEN ctr.IsActive = 1 THEN 'Yes'
WHEN ctr.IsActive = 0 THEN 'No' END AS PoweredOn
,CASE WHEN lastTime.Event = 'Logoff' THEN 'No'
WHEN lastTime.Event = 'Logon' THEN 'Yes'
ELSE 'N/A' END AS UserLoggedOn
FROM vRM_Computer_Item ci
JOIN Inv_Client_Task_Resources ctr
ON ctr._ResourceGuid = ci.Guid
LEFT JOIN (SELECT _ResourceGuid, _eventTime, clo.[Event]
FROM Evt_AeX_Client_LogOn clo
JOIN (SELECT MAX (_id) AS ID
FROM Evt_AeX_Client_LogOn
GROUP BY _ResourceGuid) maxid
ON maxid.ID = clo._id) lastTime
ON lastTime._ResourceGuid = ctr._ResourceGuid