In my opinion, McAfee is a piece of junk if your operating system is ME. I know that's a hard pill to swallow because of their reputation of being one of the TOP Antivirus programs, but I would have to say YES, McAfee is part of your problem, it was for my system anyways, in fact, I had purchased their program and after running it I truly believe that they helped in giving me more Viruses. After I explained the problems I was having from their program, they refunded all of my money and after I uninstalled McAfee, my system ran much better, although I had other problems too. It also sounds like your infested with god only knows what, it also sounds like you need a Registry Clean and Cleaner. I have a article I received from Downloads.com I can give you on how to use a cleaner that was suggested from one of their Experts for your system, if you give me your E-mail addy I will forward it to you, it greatly helped me with cleaning my registry and other things that needed a cleanup.
Tina, if you don't have any good Spyware programs running on your system, that can also pose a problem. Another thing that can slow your system down are large files, like music or videos, you know things like that. Do a "Thorough Scan Disk" and "Defrag", that also helps. When you do a Defrag, do it on both the "C" and "D" drives.
All of the above helped my system to run really well.