McAfee Site Advisor is an add-on for IE. I don`t know what is causing your problem but it would be an idea to check first that it is actually enabled.
IE> Tools> Manage Add-ons> Enable or disable add-ons.
See if it is enabled or not. It could be that something nasty has turned it off in which case turning it back on may not be enough and you may have to run Malwarebytes Anti-malware to check things out.