Can you answer a few questions please?
1. What is your operating system and service pack and are you up to date?
2. What are your computer's CPU and RAM and hard drive free space details?
3.. If you had security software installed previously have you used the appropriate removal tool?
4. How old is this Antivirus Plus CD?
Apart from the fact that you should have Service Pack 1 (SP1) installed, help with that here: https://community.mcafee.com/docs/DOC-2205 plus Internet explorer 9, whether ot not you use it. I can't think what is wrong.
The best choice now would be to contact Technical Support by phone or online chat, it's free and linked under Usefgul lINKS AT THE TOP OF THIS PAGE.
However I recommend you install the Service Pack and IE9 and make sure any applicable updates after that are also installed and make sure Flash, Shockwave etc. are up to date (Adobe.com) and Java is also up to date (java.com) as McAfee relies on IE9 regardless of your default browser choice - first before contacting support.