When you installed it did you already have some security software installed such as, for example, Malwarebytes? This can happen, the software appears to install but actually fails at next reboot. This is something we want McAfee to adjust so that if the software dislikes something it should indicate that you should first remove it, thenh continue.
If this is the case remove the other software and try it again.
Any problems Technical Support will help you by phone or online chat linked under Useful Links at the top of this page.