There may be various reasons for the installation to fail. So please clarify/try the below:
• Please let us know your computer’s configuration (E.g.: CPU, Memory & Operating System). To check that please make a single right click on My Computer>Click on Properties> Click on General Tab
• Are you trying to install the McAfee for the 1st time? If so did you use any other security programs to the computer?
• Checked for the installed programs in the computer – If you find any other security programs like Symantec, AVG, Trend Micro, Spy Blaster etc – Uninstall them from Control Panel> Add/Rem
• Run the McAfee Pre-Install Tool from http://download.mcafee.com/products/licensed/cust_support_patches/McPreInstall.exe
• Also run the McAfee removal tool from http://download.mcafee.com/products/licensed/cust_support_patches/MCPR.exe
to remove all the traces from the computer, reboot the computer and then try the installation