First make sure that it isn't still installed and maybe just corrupted somehow.
Go to Control Panel > Programs and if McAfee is listed uninstall it then run the MCPR cleanup tool and reboot.
Then go HERE and download your software again (you'll need to log in with whatever email and password you originally used, there's a link if you've forgotten the details).
Or if you get the software from your computer maker or ISP go to their website.
If you have problems locating your account speak to Customer Service by phone or online chat.. It's free of charge.