The software is compatible with all Windows OS's both 32-bit and 64-bit, except for 64-bit XP so there shouldn't be a problem. Is this Windows 7 SP1? You can check that by right-clicking Computer and selecting Properties. Also as McAfee uses Internet Explorer for display purposes make sure you are up to date with IE9 and all associated patches even if you use another browser as your default.
Do you have any other security software present that may interfere with it? Or did you have some and uninstalled? If the latter please run their removal tool if any. Try running the Virtual Technician to see if it will autofix any issues: http://mvt.mcafee.com/