Please clarify/perform the steps given below.
Did you made any changes to the computer in recent past?
Did you experience any spyware alert or advertisement in the computer?
Please provide us the version of McAfee product installed in the computer (Open McAfee security center-click on about in bottom left hand panel-check the build version for each product installed)?
Try to perform the Manual update through the update button in the home page of McAfee security center
Give us the error message that you get in the right hand panel of security center (ex: Detection signature file is outdated or more that 30 day old ….)
Perform the MVT in the computer and post the session ID http://mvt.mcafee.com/mvt/default.asp