On Windows XP machines, especially after reformatting and reinstalling, you need to make sure that you have Java and the new Windows Scripting engine installed. Also be sure that the Internet Explorer Security settings allow for ActiveX to be "Enabled". Because McAfee's site requires those to be running, then you'll need them set up that way. Use the links below to install them:
First, try installing the new Windows Script Engine from the link below. After doing so, see if you can access the site.
Windows Script 5.6 for Windows 2000 and XP
If that doesn't get it doen, then
Click on the Sun Java download site below. Once there, click on the "Download J2SE JRE" link beneath the "J2SE v 1.4.2_06 JRE includes the JVM technology" section and proceed through the windows to download the "Windows Offline" installer file. Once it's on your desktop, shut down all background programs, then double click on the file to install it.
J2SE v 1.4.2_06 JRE
"If the above steps don't get it done, then the sites have probably been added to a HOSTS file or some other site blocking program on the computer".