Do This, First go to Control Panel Double Click Add Remove Programs Icon click on Mcafee click remove. Then go to Start Search type Mcafee on C:\ drive if that's where you installed it, then delete all Mcafee that it finds. You could then do this. To clear it.
Next go to start run type regedit and press enter, go to menu under edit click find in the box type Mcafee and press enter it will bring up only one entry at a time, press delete key then click ok to confirm to go to next entry press F3 and delete do this until you get to the end of the registry. DO NOT TOUCH ANYTHING ELSE IN THE REGISTRY other than Mcafee then reboot your computer