Please try to uninstall your software by going to Add/remove programs and reboot the computer. Then run the MCPR removal tool and reboot again. MCPR found at the top of this page under Useful Links. http://service.mcafee.com/FAQDocument.aspx?lc=1033&id=TS101331 will assist you as well
Run the McAfee preinstall tool http://download.mcafee.com/products/licensed/cust_support_patches/Mcpreinstall.e xe
Login to your online McAfee account and download and install your software and see if the issue is resolved.
If still having trouble then please contact Technical Support and they can troubleshoot further and have many more tools available to diagnose problems.
Please confirm whether a System Restore was done recently on your machine. It will be more helpful if you could post the version of McAfee installed on your PC. (Open McAfee User Interface > Click on About at the bottom right > Post back Security Center version and VirusScan version)
Also ensure that you don't have any other AV applications installed apart from McAfee.
Selvan is a technician from McAfee who needs an answer to continue helping you with your issue. Could you please respond to him?