What is your operating system and service pack and are you totally up to date?
Check your system clock for accuracy both time and timezone-wise.
As McAfee relies heavily on a working Internet Explorer set at default settings (whether or not it is your default browser) go to Internet Explorer Tools/Internet Options.
If IE6: Security tab - set all zones to default, Content tab - turn off Content Advisor (if on), Advanced tab - set to default. Apply those changes if any and OK it.
If IE7 or 8 (which you should by now have upgraded to) - go to the Advanced tab and click "Reset". then Apply and OK any prompts.
Close and reopen IE and re-enable your add-ons under Tools/Manage Add-Ons.
Then do the following:
1. Uninstall all McAfee programs through "Add or Remove Programs" in Windows "Control Panel".
2. Use the MCPR tool, see this article:
How to remove supported McAfee consumer products using the McAfee Consumer Products Removal tool (MC... This will remove all McAfee remnants from your computer. (you must have Windows Vista, XP or 2000 SP4 to use this tool)
3. Launch Windows Explorer and delete all McAfee files in "Program Files" but especially in "C:\Document and Settings\<user>\Application Data" and "C:\Document and Settings\All Users\Application Data". You have to set Windows Explorer to show all hidden files and folders (Tools > Folder Options > View tab). Just delete the McAfee folders even if they are empty in all the "Application Data" folders. Can be more than one!
In Vista: C:\Program Files, C:\ProgramData and C:\Users\yourname\AppData\Roaming
If you can't find these files don't worry. It just means that MCPR has done its job.
4. Reboot and redownload/reinstall your McAfee products directly from your account at the McAfee web site.
If you are McAfee direct customer, go to
https://home.mcafee.com/Secure/Protected/Login.aspx and log in to download your McAfee products.
If you received your McAfee products from your service provider, please use the list below to download your software.
Comcast users should go to
http://security.comcast.net/ and log in to download your software.
DELL users should go to
https://us.mcafee.com/root/login.asp?affid=105 and log in to download your software.
Gateway users should go to
https://us.mcafee.com/root/login.asp?affid=370 and log in to download your software.
eMachines users should go to
https://us.mcafee.com/root/login.asp?affid=365 and log in to download your software.
MSN users should go to
http://membercenter.msn.com/ and log in to download your software.
AOL users should go to
http://daol.aol.com/security/ and log in to download your software.