You don't mention what operating system and service pack this is but I would reinstall IE8 if I were you as McAfee relies on an up-to-date IE set to its defaults in order to operate normally. Don't go for IE9 beta as that is incompatible and will be until it's final.
I see by your email address that you appear to be at an educational institution and am wondering if you use your machine behind their proxy/firewall? If so this has always been a major stumbling block and you should first contact their IT department for any helpful hints at getting around the proxy, or contact McAfee Technical Support Chat via Useful Links at the top of this page.
If you want a good anti-malware application to keep handy for emergencies I use the FREE version of THIS one.
Always update it before running and let it remove anything it finds and reboot immediately if asked to.