What McAfee software? Name and version would help...open it and click About.
Also what is the computer make and model, operating system and service pack (if applicable), what amount of free hard drive space and installed memory do you have?
I assume you tried uninstalling via Control Panel, what error did it give?
Have you had any infection or run any registry cleaners lately?
Please post back the Version of McAfee Installed on your PC. Operating System info will also be much helpful. I assume that you are on a high speed internet connection preferably wired.