What is the operating system u hav (windows xp , windows vista or windows 7).
It depends on your ram memory size and the startup options that are enabled . to check the ram size go to start > right click "computer(my computer)" then select properties .
if you want to have mcafee displayed whenever system boots then try to click go to Start > Run (or press Windows-R) > type " msconfig " then the startup tab at the extreme right u can enable mcafee services there but before doing that make sure u hav higher ram memory size . so that system wont slowdown when system is started .