I had similar problems last year and when I contacted McAfee was advised that it was the Firewall product "interacting" with AOL my ISP ... I uninstalled the Firewall and since then all has worked perfectly. I buy the McAfee Clinic each year and have found updates and stuff excellent ... just the Firewall was a snag!
Mind you - I am always grumbling at how slow my puter is and am blaming all the £$%* that starts on StartUp which I don't know how to prevent!! ... duh!