Moved to your own thread as the one you posted to is 4 years old and the reasons for the symptoms are most likely different, plus your OS certainly is.
Was Window 8 by any chance an upgrade from an earlier Windows? This often corrupts security software and it's always wise to uninstall it first, reinstall afterwards.
It might help to know what version of software you have. Open it and click About and post details for SecurityCenter and VirusScan please.
First you could try running the Virtual Technician to see if it finds and fixes any issues. http://mvt.mcafee.com/
If that fails to help then go to Programs and uninstall McAfee
Then run the MCPR cleanup tool: http://download.mcafee.com/products/licensed/cust_support_patches/MCPR.exe
Reboot and reinstall from your online account.